NCERT Solutions For Class 8 Science Chapter 4 Materials : Metals and Non-Metals

Correct option is (a) Zinc.

Explanation: Generally metals can be beaten into sheets. Zinc is a metal while phosphorus, sulphur and oxygen are non-metals.

To polish gold jewellery, it is dipped in a mixture of acids called aqua regia (a mixture of hydrochloric acid and nitric acid). The outer layer of gold jewellery dissolves in the acid mixture and the inner shiny layer appears. Due to dissolution of upper layer of gold, its weight gets reduced.

No, lemon pickle cannot be stored in an aluminium utensil. This is because lemon pickle contains acid which reacts with aluminium (metal) to liberate hydrogen gas. The liberated hydrogen gas can spoil lemon pickle.

(a) Aluminium is a highly malleable cheap metal which does not react with food items. Therefore, aluminium foils are used to wrap food items.

(b) Metals are good conductors of heat and electricity. Therefore, immersion rods used for heating liquids are made up of metallic substances.

(c) A less reactive metal cannot replace more reactive metal from its salt solution. Since, copper is less reactive than zinc, therefore, it cannot replace zinc from its salt solution.

(d) Sodium and potassium are very reactive metals. They react vigorously with oxygen and water. A lot of heat is generated in the reaction. If kept in open, they react with oxygen and moisture present in air and catch fire immediately. Therefore, sodium and potassium are stored in kerosene.

(a) Generally, non-metals react with acids.                              (F)

(b) Sodium is a very reactive metal.                                        (T)

(c) Copper displaces zinc from zinc sulphate solution.             (F)

(d) Coal can be drawn into wires.                                             (F)

(a) reactive

(b) good,  electricity

(c) more

(d) hydrogen

Correct statement is option (c), Generally, metals are ductile.

Explanation: Mercury is a metal but it cannot be drawn into wires because it is liquid at room temperature. Therefore, it is non-ductile.

(a) To find the nature of the gas, add a small amount of water into the test tube in which gas is collected. Quickly cover the test tube and shake it well. Now test the solution with red and blue litmus paper one by one. You will observe that solution turns blue litmus red while red litmus remains unaffected. This confirms that gas evolved during burning of charcoal is acidic in nature.

(b) Name of the product formed in the reaction of charcoal with oxygen is carbon dioxide.

When carbon dioxide is dissolved in water, carbonic acid is formed. The carbonic acid turns blue litmus paper red. Generally, oxides of non-metals are acidic in nature.

(a) When sulphuric acid is poured on a copper plate, the copper metal reacts with sulphuric acid to form copper sulphate and hydrogen gas.

(b) Iron is more reactive than copper therefore, it displaces copper from copper sulphate solution to form iron sulphate.

Initially, copper sulpahte solution is blue in colour. when iron nail is placed in it, the blue colour of copper sulphate solution fades. The solution turns green due to formation of iron sulphate. Copper gets deposited on iron nail.