CBSE Sample Papers For Class 10 Science Mock Paper 1

Q1. A student burned some sulphur powder in a spoon and collected the gas in a gas jar.
(a) What happens when a dry and moist litmus paper is brought near the mouth of the gas jar?
(b) Write the chemical reaction that occurs when water is added into the gas jar.

OR

​A student immersed an iron nail in a copper sulphate solution and kept the solution for some time. What changes were observed? Identify the type of reaction involved.​

Ans:

(a) Sulphur reacts with oxygen in the air to form sulphur dioxide. The gas does not affect dry litmus paper. When moist litmus paper is brought near SO₂, it combines with water to form sulphurous acid which turns blue litmus to red.
(b) The reaction of sulphur dioxide with water takes place to form sulphurous acid.

SO2(g)+H2O(l)→H2SO3(aq)\rm S{O_2}\left( g \right) + {H_2}O\left( l \right) \xrightarrow{\hspace*{.3cm}}{H_2}S{O_3}\left( {aq} \right)

SO2​(g)+H2​O(l)​H2​SO3​(aq)
OR

When the iron nail was immersed in copper sulphate solution, iron displaced copper from copper sulphate solution. As a result, the blue colour of the copper sulphate solution disappeared and the solution turned light green due to the formation of ferrous sulphate. A reddish-brown coating of copper metal was formed on the surface of the iron nail.

BlueCuSO4​​(aq)+Fe(s)→GreenishFeSO4​(aq)​+ReddishbrownCu(s)​

The reaction is a displacement reaction.

Q2. Answer the following questions:
a) Mention any one point of difference between voluntary and involuntary muscles.
b) How muscles change their shape when nerve impulses reach them?

Ans:

a)

Voluntary Muscles	Involuntary Muscles
These muscles are under our control	These muscles are not under our control

b) Muscle cells have special proteins which change their shape and arrangement in the cell in response to nervous electrical impulses. The new arrangement of these proteins provides a shorter form to the cells.

Q3. Describe what happens to the eaten food in stomach?

Ans:

The gastric glands present in the wall of the stomach release HCl, pepsin, and mucus.

– HCl creates an acidic medium in the stomach to facilitate the action of the enzyme pepsin.

– Pepsin is an enzyme that digests the protein present in the eaten food.

– Mucus protects the lining of the stomach from the acidic action of HCl.

Q4. Answer the following questions:
a) Define blood pressure.
b) Identify the type of blood vessel in which blood pressure is very high.
c) Name an instrument used for measuring blood pressure?
d) How is systolic pressure different from diastolic pressure?

Ans:

a) The force exerted by the blood against the wall of a vessel is called blood pressure.
b) Artery is a type of blood vessel in which blood pressure is very high.
c) Sphygmomanometer is an instrument used for measuring blood pressure.
d)

Systolic pressure	Diastolic pressure
The pressure of blood inside the artery during ventricular contraction is called systolic pressure.	The pressure of blood inside the artery during ventricular relaxation is called diastolic pressure.

Q5. The position of an object kept on a surface in front of a plane mirror is shown in the figure.

If the object is displaced to another point (say B) having co-ordinates (-1,-3).
Calculate the distance between the initial position of the object and final position of image formed by the plane mirror.

OR

The optical prescription for a pair of spectacles for the left and the right eye are –2.5 D and –4 D respectively.

a. For which eye, the lens has a greater focal length?

b. Among the two lenses which lens is thinner at the middle?

Ans:

Old position of the object,  A(2,3)
Final position of the object, B(-1,-3)

Distance of image from the mirror = Distance of object from the mirror
Hence, the co-ordinate of the image will be (1, -3).
)Distance between the two positions can be obtained from the distance formula, that is

AC=(x2−x1)2+(y2−y1)2=(1−2)2+(−3−3)2=37units \begin{array}{l}{AC\hspace{0.33em}=\hspace{0.33em}}\sqrt{{\left({{x}}_{{2}}-{{x}}_{{1}}\right)}^{{2}}{+}{\left({{y}}_{{2}}-{{y}}_{{1}}\right)}^{{2}}}\\ {\hspace{0.33em}\hspace{0.33em}\hspace{0.33em}\hspace{0.33em}\hspace{0.33em}=\hspace{0.33em}}\sqrt{{\left({1}-{2}\right)}^{{2}}{+}{\left(-{3}-{3}\right)}^{{2}}}\\ {\hspace{0.33em}\hspace{0.33em}\hspace{0.33em}\hspace{0.33em}\hspace{0.33em}=\hspace{0.33em}}\sqrt{{37}}{\hspace{0.17em}units}\end{array}

AC=(x2​−x1​)2+(y2​−y1​)2​=(1−2)2+(−3−3)2​=37​units​

OR

(a) The focal length is the inverse of the power of the lens. So, the focal length of the lens with less power would be higher. So, the focal length of the lens having power –2.5 D is greater. During the comparison of the power of lenses, the magnitude of power is only considered.

(b) Both the lenses are thinner in the middle as the focal length is negative. Both lenses are concave.

Q6. What would happen if ozone layer did not exist on earth?

Ans: Ozone layer protects humans and other living organisms from harmful ultraviolet (UV-B) rays of the sun. In the absence of ozone layer, the harmful effects of UV rays will lead to an increased number of serious health risks for humans. There will be an increase in the incidences of sunburns, skin cancer, and cataract. It will also affects the crop yield. It will also cause a serious damage to biodiversity. An increased UV-B rays will reduce the level of planktons in oceans, subsequently diminishing fish stocks.

Q7. Segregate the reactants and products for the following chemical reactions.

H2+Cl2→2HClC+O2→CO2

Opt:

Reactants	Products
H2, Cl2 and HCl	C, O2 and CO2

 

Reactants	Products
HCl and CO2	H2, Cl2, C and O2

 

Reactants	Products
H2, Cl2, C and O2	HCl and CO2

 

Reactants	Products
C, O2 and CO2	H2, Cl2 and HCl

Ans:

Reactants	Products
H2, Cl2, C and O2	HCl and CO2

Q8. When copper is heated in air

Opt:

CuO is formed

Cu₂O₂ is formed

Cu₂O is formed

CuO₂ is formed

Ans: CuO is formed

Q9. Identify the substance oxidised and reduced in the given chemical equation.

MnO2+ 4HCl→MnCl2+ 2H2O + Cl2

Opt:

Oxidised-HCl
Reduced-MnO₂

Oxidised-MnO₂
Reduced-HCl

Oxidised-MnCl₂
Reduced-H₂O

Oxidised-MnCl₂
Reduced-Cl₂

Ans:

Oxidised-HCl
Reduced-MnO₂

Q10. Sodium hydroxide is obtained on a large scale

Opt:

from brine solution or sea water

by dissolving sodium metal in water

by direct combination of sodium and chlorine

by direct combination of sodium, oxygen and hydrogen

Ans: from brine solution or sea water

Q11. Which of the following statements is TRUE regarding homologous series?

Opt:

Subsequent members of the homologous series differ by a molecular mass of 16u.

Subsequent members of the homologous series differ by a molecular mass of 24u.

Subsequent members of the homologous series differ by a molecular mass of 28u.

Subsequent members of the homologous series differ by a molecular mass of 14u.

Ans: Subsequent members of the homologous series differ by a molecular mass of 14u.

Q12. A milkman adds a very small amount of baking soda to fresh milk to

Opt:

produce froth

kill bacteria

make it acidic

make it alkaline

Ans: make it alkaline

Q13. Match the following hydrocarbons in column I with their correct structures in column II:

Column I	Column II
a) Alkyne	i) –C–C–
b) Acyclic alkane	ii) –C=C–
c) Cycloalkane	iii) –C≡C–
d) Alkene	iv)

Opt:

(a)-(iii), (b)-(ii), (c)-(iv), (d)-(i)

(a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)

(a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)

(a)-(iv), (b)-(ii), (c)-(iii), (d)-(i)

Ans:

(a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)

Q14.

Two test tubes are filled with water. In test tube A, a leafy twig is placed and test tube B is without the twig. A layer of oil is added over the surface of the water in both the test tubes. The setup is placed in the sunlight for three days. Predict what will happen after three days.

Opt:

The water level in test tube A and B will decrease.

The water level in test tube A and B will be the same.

The water level will increase in test tube A and will decrease in test tube B.

The water level will decrease in test tube A and will remain the same in test tube B.

Ans: The water level will decrease in test tube A and will remain the same in test tube B.

Q15. Identify the part of a leaf from where gaseous exchange takes place.

Opt:

1

2

3

4

Ans: 4

Q16. Mendel experimented by using two pea plants with contrasting traits (tall and short plants). Which of the following options CORRECTLY describes the F₁ generation?

Opt:

All the plants are tall.

All the plants are short.

The plants are tall and short in a ratio of 3:1.

The plants are tall and short in a ratio of 1:3.

Ans: All the plants are tall.

Q17. Read the given sentences carefully and choose the correct option.
A: A person suffering from diabetes has a high level of insulin in his blood.
B: Insulin stimulates the absorption of glucose from the blood into the body cells.

Opt:

Both A and B are true and B is the correct explanation of A.

Both A and B are true but B is not the correct explanation of A.

A is true but B is false.

A is false but B is true.

Ans: A is false but B is true.

Q18. The given image is showing a type of pollination. Which of the following statements is correct about the given mode of pollination?

Opt:

The cross-pollinated flowers show wide variations in their characteristics.

The cross-pollinated flowers show less variations in their characteristics.

The cross-pollinated flowers are dull coloured and without nectar.

The cross-pollination occurs between plants of different species.

Ans: The cross-pollinated flowers show wide variations in their characteristics.

Q19. Statement A: The electrical resistance of insulators is higher than that of alloys.

Statement B: The heating element of an electric iron is made up of aluminium.

For the given statements please choose the correct option.

Opt:

Both statements are true.

Both statements are false.

Statement A is true, but statement B is false.

Statement A is false, but statement B is true.

Ans: Statement A is true, but statement B is false.

Q20. A fuse wire is a wire of __________________.

Opt:

low resistance and low melting point

high resistance and high melting point

high resistance and low melting point

low resistance and high melting point

Ans: high resistance and low melting point

Q21. If we consider two stream of electrons which move parallel to each other in opposite directions, then these ​

Opt:

​repel each other​

​attract each other​

​do not exert any force on one another​

​get rotated to be perpendicular to each other​

Ans: repel each other​

Q22. Identify the properties of a proton that may change when it moves freely in a magnetic field.
a. Mass
b. Velocity
c. Momentum
d. Charge

Opt:

a and b

b and c

a and d

a and c

Ans: b and c

Q23.

A compound X on dehydration with conc. H₂SO₄ forms Y with a molecular mass of 42 g. X decolourises alkaline KMnO₄ solution to form an oxidised product Z. Identify X, Y and Z.

Opt:

X – C₂H₅OH, Y – C₂H₄, Z – CH₃COOH

X – C₃H₇OH, Y – C₃H₆, Z – C₂H₅COOH

X – C₃H₇OH, Y – C₂H₅OH, Z – C₃H₇COOH

X – C₃H₈, Y – C₃H₆, Z – C₂H₅COOH

Ans: X – C₃H₇OH, Y – C₃H₆, Z – C₂H₅COOH

Q24.

Read the below-given sentences carefully and choose the correct option.
Assertion (A): Bacteria inhabit the most inhospitable habitats like hot springs, deep-sea thermal vents etc.
Reason (R): Bacteria have complex body design.

Opt:

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A is true but R is false.

A is false but R is true.

Ans: A is true but R is false.

Q25. Read the given statements carefully and select the correct option.
Assertion (A): Zooplankton is the primary consumer in the marine ecosystem.
Reason (R): Zooplankton feeds off photosynthesising bacteria known as phytoplankton.

Opt:

Both A and R are true, and R is the correct explanation for A.

Both A and R are true, but R is not the correct explanation for A.

A is true, but R is false.

A is false, but R is true.

Ans: A is true, but R is false.

Q26. Assertion: In a straight wire, a current is flowing parallel to the x-axis and magnetic field is there in the y-axis then the wire will experience force in the z-axis.
Reason: Direction of force can be given by Right-hand thumb rule.

Opt:

Both the assertion and the reason are true, and the reason is the correct explanation of the assertion.

Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.

The assertion is false, but the reason is true.

The assertion is true, but the reason is false.

Ans: The assertion is true, but the reason is false.

Q27. Answer the following questions:

a) Fresh milk has a pH of 6. How does its pH change when it turns into curd?

b) Explain the pH change as the cause of tooth decay. How can tooth decay be prevented?

c) How will the occurrence of photosynthesis in underwater plants change the pH of the surrounding water considering the absorption of CO₂ during the process?

Ans:

a) Fresh milk has a pH of 6. During its conversion into curd, the pH value decreases because of the formation of lactic acid.

b) Tooth enamel is composed of calcium hydroxyapatite which is the hardest substance in our body. If the pH in the mouth is below 5.5, it leads to tooth decay. It can be prevented by cleaning the mouth after having food and by brushing the teeth using toothpaste (basic) daily.

c) CO₂ is an acidic gas. Therefore, its absorption by the underwater plants during the process of photosynthesis will decrease its concentration in the surrounding water, thereby increasing its pH.

Q28. Write the balanced equation for the following chemical reactions-

(a) Sodium + Water → Sodium hydroxide + Hydrogen(b) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride(c) Hydrogen sulphide + Oxygen → Water + Sulphur dioxide

Ans:

(a) 2Na(s)+2H2O(l) →2NaOH(aq)+H2(g)(b) 3BaCl2(aq)+Al2SO43(aq)→3BaSO4(s)+2AlCl3(aq)(c) 2H2 S(g)+3O2 (g)→2H2O(l)+2SO2(g)

Q29. Read the given case and answer the following questions:

Case – An artificial kidney is used in case of kidney failure. It is a device that removes waste products from the blood through dialysis.

a. What is the structural and functional unit of the kidney?

b. What are the functions of the kidney?

c. ‘Poor kidney functioning accelerates heart problems and vice-versa’. Justify.

                                                            OR

Read the given passage and answer the following questions.

Case – Some children in a village have complained of swollen necks. More children complain of swollen necks every month. Although many people in the village relate this condition to superstition, a literate person makes the village people aware that this might be a disease that needs to be consulted with a doctor.

i. Do you agree that the problem of the swollen neck is a disease?

ii. Why is it caused?

iii. Which gland is associated with the problem of swollen neck and how is it regulated?

Ans:

a. Nephron is the structural and functional unit of the kidney.

b. Kidneys regulate water balance or osmotic pressure of the blood. They also help in urine ultrafiltration.

c. In the case of kidney failure, the heart functioning decreases due to the accumulation of toxins. Also, various kidney problems arise due to irregular lipid levels, which also lead to heart diseases.

                                                              OR

i. Yes, the problem of the swollen neck is a disease known as goitre.

ii. Goitre is caused due to the deficiency of iodine in the body.

iii. The gland associated with goitre is the Thyroid gland. The thyroid gland secretes the thyroxin hormone which helps in the metabolism of carbohydrates, fats, and proteins. Iodine is necessary for the secretion of the thyroxin hormone. Therefore, deficiency of iodine causes low secretion of thyroxin. It results in a disturbed functioning of the thyroid gland, causing goitre.

Q30. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.

Ans:

\begin{array}{l}\text{Given, focal length }\left(\text{f}\right)\text{ = +15 cm}\\ \text{ object distance }\left(\text{u}\right)\text{ = }-\text{10 cm}\\ \text{ As per mirror formula,}\\ \frac{\text{1}}{\text{v}}+\frac{\text{1}}{\text{u}}\text{=}\frac{\text{1}}{\text{f}}\\ \Rightarrow \frac{\text{1}}{\text{v}}=\frac{\text{1}}{\text{f}}-\frac{\text{1}}{\text{u}}\text{=}\frac{\text{1}}{\text{15 cm}}-\frac{\text{1}}{\left(\text{-10 cm}\right)}\text{=}\frac{\text{25}}{\text{150 cm} }\\ \; \; \; \; \; \; \; \; \text{v = 6 cm}\\ \text{As }\left(\text{v}\right)\text{ is positive hence, image is formed behind the mirror}\text{.}\\ \text{Magnification }\left(\text{m}\right)\text{=}\frac{\text{image distance}}{\text{object distance}}\text{=}-\frac{\text{v}}{\text{4}}\text{=}-\frac{\text{6}}{\left(-\text{10}\right)}\text{=+0}\text{.6}\\ \text{Here, positive sign shows that the image formed is virtual and erect}\text{.}\end{array}

Q31. If light passes from one medium to another medium, what will happen to its frequency and wavelength? How can we identify that whether a given piece of glass is a convex lens, concave lens or a plane glass piece?

Ans: When light passes from one medium to another medium, its frequency remains constant if there is no relative motion between the source and the observer. However, its wavelength changes.
Take the given glass plate over some printed letters on a paper. Glass should be close to the paper.
(1) If the letters seem to be magnified, the given glass piece is a convex lens.
(2)  If the letters seem to be diminished, the given glass piece is a concave lens.
(3) If the letters seem to be of same size, then the given glass piece is a plane glass piece.

Q32. (i) The given diagram shows the deflection in galvanometer needle when a bar magnet is brought close to a coil.

Give the direction of induced current in the given cases by drawing the appropriate direction of galvanometer needle.

(a)

(b)

(ii) (a) Replace the bar magnet in the given diagram with another coil connected to a circuit in such a way that the direction of deflection in the galvanometer is same when the key is brought to ON position.

(b) State the rule used to find the direction of induced electric current in the coil.

OR

a. Explain the phenomenon of electromagnetic induction. Also, state Faraday’s law of electromagnetic induction.

b. A conducting coil is placed near a solenoid coil. Will an electric current be induced in the conducting coil if the current carrying solenoid coil is:

1. laterally displaced with respect to the conducting coil.

2. longitudinally displaced with respect to the conducting coil.

Ans:

(i) (a) As the bar magnet moves in opposite direction, the electric current in the coil will induce in opposite direction. Thus, the galvanometer needle will also deflect in opposite direction.

(b) As the poles of the bar magnet are inverted, the electric current in the coil will also induce in opposite direction. Thus, the galvanometer needle will also deflect in opposite direction.

(ii) (a) The another coil should be connected as shown.

(b) Fleming’s right hand rule is used to find out the direction of induced electric current.

Fleming’s Right Hand Rule: Stretch the thumb, forefinger and middle finger of right hand so that they are perpendicular to each other. If the forefinger indicates the direction of the magnetic field and the thumb shows the direction of motion of conductor, then the middle finger will show the direction of induced current.

OR

a. Electromagnetic induction is the phenomenon in which an induced current and induced emf are produced in a coil by changing the magnetic field.Faraday’s based on his experiment formulated the following two laws of electromagnetic induction.

1. Whenever there is a change in magnetic flux linked with a coil, an electric current is induced. This induced current lasts so long as there is a change in the magnitude flux linked with the coil.

2. The magnitude of the induced current is directly proportional to the rate of change of magnetic flux linked with the coil.

b. Electric current will be induced in both cases when the current-carrying solenoid is moved laterally and longitudinally with respect to the conducting coil. In both cases, the magnetic field lines cross the solenoid changes which leads to the induction of current.

Q33. Answer the following questions based on this information.
(i) Why living organisms require energy?
(ii) Name the ultimate source of energy.
(iii) Which form of energy is taken up by the consumers?

Ans:

(i) Living organisms require energy to perform various activities such as growth, reproduction, metabolism etc.
(ii) the ultimate source of energy is the Sun.
(iii) Consumers (primary and secondary) use chemical form of energy.

Q34. ​Answer the following questions:
a) Why alkenes do not have a homologue with a single carbon atom?
b) State one unique property of carbon and its significance.
c) Name two elements that will only form a single covalent bond with a carbon atom.
d) Name an element that can form a double bond with carbon.
e) What is the maximum number of hydrogen atoms that can bond with a carbon atom?

OR
​Answer the following questions:
a) Give the name of the functional group which is always present in the middle of a carbon chain.
b) Draw the structures for the following compounds:
i) Ethanal ii) Propanal
iii) Butanal iv) Pentanal​

Ans:

​a) In unsaturated hydrocarbons, there needs to be at least one double (alkenes) or one triple (alkynes) bond. Such a system is not possible with a single carbon atom. Therefore, alkenes do not have a member with a single carbon atom.

b) The most unique property of a carbon atom is its ability to combine with itself and other atoms to form long chains. This property of self-combination, which is also known as catenation, is significant because it gives rise to an extremely large number of carbon compounds (or organic compounds).

c) Elements like hydrogen, and all the halogens (F, Cl, Br, I) will always form a single covalent bond with a carbon atom as their valency is one.

d) Oxygen can form a double bond with a carbon atom. e) A hydrogen atom has one valency. Therefore, four hydrogen atoms can bond with a carbon atom.

OR

a) The functional group that always present in the middle of a carbon chain is ketone group, -CO-.

b)
i) Ethanal-

ii) Propanal-

iii) Butanal-

iv) Pentanal-

Q35. Answer the following questions

1. Write any three differences between binary fission and multiple fission, in tabular form.

2. Why simple organisms are capable of producing new organisms through regeneration process but complex organisms are unable to do so?

OR

Observe the image depicting the male reproductive system shown below and answer the following questions:

(a) Identify the part labelled as “a”.

(b) What is the function of part labelled as “a”?

(c) What is the function of ejaculatory duct that is labelled as “b”?

(d) In male reproductive system, ejaculation of sperm occurs through which opening?

(e) Which gland surrounds the urinary opening in males?

Ans:

Binary fission	Multiple fission
i) The parent nucleus divides into two daughter nuclei e.g. Leishmania, Amoeba.	i) The parent nucleus divides into many daughter nuclei e.g. Plasmodium.
ii) Cytoplasm is divided into two parts which along with the divided nuclei forms two new cells.	ii) Around each daughter nucleus some amount of cytoplasm is deposited forming new cells.
iii) Daughter cells are enclosed by individual cell membrane.	iii) All daughter cells are enclosed by a common membrane. In favourable conditions, the membrane ruptures and the daughter cells are set free, acting as new individual.

 

2. Regeneration is carried out by specialized cells. These cells proliferate and make large number of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues in an organized sequence referred to as development. If these specialized cells are absent from the proliferated mass, the regeneration will not take place. The complex organisms possess these specialized cells only at certain tissue level. They have distinct levels of organisation in their organ system and all of these organ systems are linked together and work in unison. However, in simple organisms, the entire body is made up of similar kind of cells in which any body part can be formed by growth and development.

OR

(a) The part labelled as “a” is seminal vesicle.

(b) The fluid produced by seminal vesicle contains fructose, which helps to feed sperm cells so that they survive long enough in order to fertilise the egg cell.

(c) The ejaculatory duct opens and expels sperm and the secretions from the seminal vesicles into the urethra.

(d) In male reproductive system, ejaculation of sperm occurs through urethra.

(e) Prostate gland surrounds the urinary opening in males.

Q36. (i) State the law, which relates the current in a conductor to the potential difference across its ends.
(ii) Draw the V-I graphs for a
(a) Metallic conductor.
(b) Liquid Electrolyte.
(c) Vacuum tube.
(iii) A simple electric circuit has 24 V battery and a resistor of 30 ohm. What will be the current in the circuit?

Ans:

(i) Ohm’s law relates the current in a conductor to the potential difference across its ends.
The statement of which is given below, Ohm’s Law: It states that the current flowing through a conductor is directly proportional to the potential difference across its ends, keeping the temperature constant.
(ii) The V-I characteristics for metallic conductor, liquid electrolyte and vacuum tube are given below,

(iii) Here we are given with values of V and R as 24 volts and 30 ohms respectively.
We have to find out the value of I.
(iv) By Ohm’s law we have the relation, V = IR.
Therefore, I = V/R

⇒ I = (24)/(30) = 0.8 A
.
Thus, current flowing in the circuit is 0.8 A.

Q37. (i) What is rusting of iron?
(ii) Write the two necessary conditions for rusting to occur.
(iii) Write any two common methods to prevent rusting.

OR

Answer the following questions:
a) Define reactivity series. Arrange the given metals in the order of increasing reactivities towards water: Iron, Calcium, Magnesium, Sodium
b) Name two metals that can displace zinc from zinc sulphate solution.
c) Name any one metal which is more reactive than hydrogen.
d) Name a metal that can displace copper from copper sulphate solution.
e) Name a metal that can displace silver from silver nitrate solution.

Ans:

(i) The slow oxidation of iron articles by the atmospheric oxygen in the presence of water or moisture is called rusting. Iron, when exposed to moist air, reacts with oxygen and water to form reddish brown coloured hydrated iron oxide. The hydrated iron oxide is called rust.

The rusting of iron can be represented by the equation:

4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃.xH₂O

Iron  Oxygen Water     Hydrated ferric oxide

(Rust)
(ii) The necessary conditions for rusting are :
(a) Presence of moisture
(b) Presence of air
(iii) Rusting can be prevented by the following two methods:
(a) Galvanisation: It is a process of coating zinc metal over iron by electroplating.
(b) Painting or greasing: It is a process of coating the surface of the iron object with paint or grease so that air and moisture cannot come in contact.

OR

a) The arrangement of metals in the order of their increasing reactivities is called reactivity series. Increasing order of reactivity towards water: Iron < Magnesium < Calcium < Sodium
b) Two metals that can displace zinc from zinc sulphate solution are potassium and sodium.
c) Lead is more reactive than hydrogen.
d) Zinc displaces copper from copper sulphate solution.
e) Copper displaces silver from silver nitrate solution.

Q38. The two types of wheat variants grown by a farmer are as follows:
a. Drought-tolerant, rust-prone: DDrr
b. Drought-sensitive, rust-free: ddRR
i. Determine the genotypes of the gametes of type ‘a’ and ‘b’.
ii. Determine the genotype and phenotype of F₁ generation obtained by crossing type ‘a’ and ‘b’.
iii. Can you determine how the farmer can obtain a variety of wheat that is drought resistant as well as rust-free?

OR

Compute the ratio of drought-resistant rust-free to drought-sensitive rust-prone offspring obtained in the F2 generation.

Ans:

Given,
a. Genotype of drought-tolerant, rust-prone type: DDrr
b. Genotype of drought-sensitive, rust-free type: ddRR

i. The genotype of gametes of type ‘a’ will be ‘Dr’ and that of type ‘b’ will be dR.

ii.All the plants of the F₁ generation will have the genotype DdRr and their phenotype will be drought resistant and rust-free.
However, if the farmer wants the plants that are pure for these characteristics, he will have to self-fertilise the offspring of F₁ generation.
The plants with genotype DdRr will produce the following gametes:
DR, dR, Dr, and dr

iii. The farmer can obtain a variety of wheat that is drought resistant as well as rust-free by self-pollinating F₁ individuals. F₂ generation obtained by selfing F₁ individuals will have the following genotypes:

Gametes	DR	dR	Dr	dr
DR	DDRR	DdRR	DDRr	DdRr
dR	DdRR	ddRR	DdRr	ddrr
Dr	DDRr	DdRr	DDrr	Ddrr
dr	DdRr	ddRr	Ddrr	ddrr

The plants with genotype DDRR will be pure for the two characteristics and can be bred for generations with all progenies having the same characteristics.

OR

F₂ generation obtained by selfing F₁ individuals will have the following genotypes:

Gametes	DR	dR	Dr	dr
DR	DDRR	DdRR	DDRr	DdRr
dR	DdRR	ddRR	DdRr	ddrr
Dr	DDRr	DdRr	DDrr	Ddrr
dr	DdRr	ddRr	Ddrr	ddrr

The phenotypic ratio of the F₂ generation is 9:3:3:1
Variants that are drought-resistant rust-free are 9
Variants that are drought-resistant rust-prone are 3
Variants that are drought-sensitive rust-free are 3
The variant which is drought-sensitive rust-prone is 1
The ratio of drought-resistant rust free to drought-sensitive rust-prone is 9:1.

Q39. Mohan asked for five spherical lenses ‘P’, ‘Q’, ‘R’, ‘S’ and ‘T’ of powers 4 D, – 5.5 D, 1 D, – 2 D and 5 D, respectively from a shopkeeper. The shopkeeper gave him the convex or concave lenses, as per the requirement. However, Mohan got confused as the shopkeeper gave him lenses just by looking at the values of their powers and without confirming their type.
(i) How did the shopkeeper judge the type of each lens by looking at its power? Also, classify the lenses into concave and convex lenses.
(ii) Name the lenses with the highest diverging and converging abilities and also give reasons for the same. What are the uses of a concave lens?
(iii) Calculate the power and focal length of combination of lenses.

Ans:

(i) The shopkeeper judged the type of each lens by looking at its positive or negative power. The lens with the positive power is a convex lens and the lens with the negative power is a concave lens. Thus, the lenses, ‘Q’ and ‘S’ are concave lenses and the lenses ‘P’, ‘R’ and ‘T’ are convex lenses.

(ii) The concave lens acts as a diverging lens, whereas a convex lens acts as a converging lens. Out of the concave lenses, ‘Q’ and ‘S’, Q has the highest diverging ability as the magnitude of its power is greater than that of ‘S’. Similarly, lens ‘T’ has the highest converging ability out of convex lenses ‘P’, ‘R’ and ‘T’ because of its greater magnitude of power.
Uses of a concave lens:
(a) It is used in spectacles for the correction of the defect of vision called myopia.
(b) It is used as an eye-lens in Galilean telescope.
(c) It can be combined with a convex lens in order to get high quality lens system for optical instruments.
(d) It is used in wide-angle spyhole in doors.

${(iii) Let the various powers of the lenses be given by,}\phantom{\rule{0ex}{0ex}}{{P}}_{1}\quad =4\quad \mathrm{D}\phantom{\rule{0ex}{0ex}}{\mathrm{P}}_{2}=-5.5\quad \mathrm{D}\phantom{\rule{0ex}{0ex}}{\mathrm{P}}_{3}\quad =1\quad \mathrm{D}\phantom{\rule{0ex}{0ex}}{\mathrm{P}}_{4}=-2\quad \mathrm{D}\phantom{\rule{0ex}{0ex}}{\mathrm{P}}_{5}=5\quad \mathrm{D}\phantom{\rule{0ex}{0ex}}\mathrm{Powers}\quad \mathrm{of}\quad \mathrm{combination}\quad \mathrm{of}\quad \mathrm{lenses}\quad \mathrm{is}\quad \mathrm{the}\quad \mathrm{algebric}\quad \mathrm{sum}\quad \mathrm{of}\quad \mathrm{the}\phantom{\rule{0ex}{0ex}}\mathrm{powers}\quad \mathrm{of}\quad \mathrm{individual}\quad \mathrm{lenses}\quad \mathrm{placed}\quad \mathrm{in}\quad \mathrm{closed}\quad \mathrm{contact}.\phantom{\rule{0ex}{0ex}}\therefore \mathrm{P}={\mathrm{P}}_{1}+{\mathrm{P}}_{2}+{\mathrm{P}}_{3}+{\mathrm{P}}_{4}+{\mathrm{P}}_{5}\phantom{\rule{0ex}{0ex}}\quad \quad \quad \quad \quad \quad \quad =\quad 4\mathrm{D}+\quad (-5.5\mathrm{D})+1\mathrm{D}+(-2\mathrm{D})+5\mathrm{D}\phantom{\rule{0ex}{0ex}}\quad \quad \quad \quad \quad \quad \quad =[4-5.5+1-2+5]\quad \mathrm{D}\phantom{\rule{0ex}{0ex}}\quad \quad \quad \quad \quad \quad \quad \quad =2.5\quad \mathrm{D}\phantom{\rule{0ex}{0ex}}\mathrm{Now},\quad \mathrm{power}\quad \mathrm{P}\quad =\quad \frac{1}{\mathrm{f}\quad (\mathrm{in}\quad \mathrm{metres})}\phantom{\rule{0ex}{0ex}}\therefore \quad \mathrm{Focal}\quad \mathrm{length}\quad \mathrm{of}\quad \mathrm{the}\quad \mathrm{combination}\quad \mathrm{of}\quad \mathrm{lenses},\phantom{\rule{0ex}{0ex}}\mathrm{f}=\frac{1}{\mathrm{P}}\phantom{\rule{0ex}{0ex}}\quad \quad =\frac{1}{2.5\quad \mathrm{D}}\phantom{\rule{0ex}{0ex}}\quad \quad =0.4\quad \mathrm{m}$

(iii) Let the various powers of the lenses be given by,P1​=4DP2​=−5.5DP3​=1DP4​=−2DP5​=5DPowersofcombinationoflensesisthealgebricsumofthepowersofindividuallensesplacedinclosedcontact.∴P=P1​+P2​+P3​+P4​+P5​=4D+(−5.5D)+1D+(−2D)+5D=[4−5.5+1−2+5]D=2.5DNow,powerP=f(inmetres)1​∴Focallengthofthecombinationoflenses,f=P1​=2.5D1​=0.4m