CBSE Class 12 Micro Economics Revision Notes Chapter 2 Theory of Consumer Behaviour

CBSE Class 12 Micro Economics Revision Notes Chapter 2 explain Theory of Consumer Behaviour through utility, preferences, budget, demand and elasticity. For CBSE 2026 Microeconomics, Theory of Consumer Behaviour shows how a consumer chooses the best affordable bundle.

Why does a consumer buy fewer mangoes when their price rises, or choose more bananas when they become cheaper? The NCERT Class 12 Microeconomics chapter Theory of Consumer Behaviour answers this through income, prices, preferences and satisfaction. A consumer wants maximum satisfaction, but choices stay limited by income and market prices.

The chapter explains consumer choice through two approaches: cardinal utility analysis and ordinal utility analysis. Cardinal analysis uses total utility and marginal utility, while ordinal analysis uses indifference curves and budget lines. These class 12 microeconomics chapter 2 theory of consumer behaviour notes follow the NCERT 2026 flow from utility to consumer optimum, demand curve, market demand and price elasticity of demand.

Key Takeaways

• Marginal utility rule: MU becomes zero when total utility stops rising from an additional unit.
• Budget constraint: A consumer can buy bundle (x1, x2) only when p1x1 + p2x2 ≤ M.
• Consumer optimum: The best bundle lies where the budget line is tangent to an indifference curve.
• Elasticity measure: Price elasticity of demand compares percentage change in demand with percentage change in price.

CBSE Class 12 Micro Economics Revision Notes Chapter 2 Structure 2026

Consumer Choice and Utility

Utility is the want-satisfying capacity of a commodity. In Theory of Consumer Behaviour, utility explains why a consumer prefers one bundle over another.

The NCERT chapter begins with the consumer’s problem of choice. A consumer chooses from affordable bundles according to income, prices and preferences.

Consumption bundle

A consumption bundle is a combination of two goods. NCERT uses bananas and mangoes to explain this idea.

If x1 represents bananas and x2 represents mangoes, then (x1, x2) represents one bundle. For example, (5, 10) means 5 bananas and 10 mangoes.

Utility

Utility is subjective because different consumers get different satisfaction from the same commodity. A chocolate lover may get more utility from chocolate than someone who dislikes it.

Utility also changes with place and time. A room heater gives more utility in Ladakh during winter than in Chennai during summer.

Cardinal and ordinal utility

Cardinal utility analysis assumes utility can be measured in numbers. A consumer may be said to get 50 units of utility from a shirt.

Ordinal utility analysis assumes utility can be ranked. A consumer can say which bundle gives more satisfaction, without measuring utility in numbers.

Total Utility and Marginal Utility

Total utility is the total satisfaction from consuming a fixed quantity of a commodity. Marginal utility is the change in total utility from one additional unit.

Utility analysis class 12 microeconomics questions often ask the link between TU and MU. This link explains why demand curves usually slope downward.

Total utility

Total utility from n units is written as TUn. It increases when the consumer gets more satisfaction from additional units.

Formula:

TUn = MU1 + MU2 + MU3 + ... + MUn

This means total utility equals the sum of marginal utilities from all consumed units.

Marginal utility

Marginal utility is the additional utility from consuming one more unit of a commodity.

Formula:

MUn = TUn − TUn−1

Example:

If TU from 4 bananas is 28 and TU from 5 bananas is 30, then:

MU5 = TU5 − TU4

MU5 = 30 − 28

MU5 = 2

Law of diminishing marginal utility

The law of diminishing marginal utility says marginal utility falls as consumption of a commodity increases. Other commodity consumption remains constant.

When a consumer already has more bananas, the desire for one more banana becomes weaker. This causes MU to decline with additional units.

Demand Curve from Utility Analysis

Demand is the quantity a consumer is willing and able to buy at given prices and income. A demand curve shows quantities demanded at different prices.

The downward slope of the demand curve can be explained through diminishing marginal utility. A consumer pays less for additional units because each additional unit gives lower MU.

Meaning of demand

Demand depends on the price of the good, prices of related goods, income and preferences. A consumer must be willing and able to buy the commodity.

Demand is different from desire. A desire becomes demand only when purchasing power supports it.

Law of demand

The law of demand states that demand and price usually move in opposite directions. Other things remain constant.

When price rises, quantity demanded falls. When price falls, quantity demanded rises.

Why the demand curve slopes downward

Each additional unit gives lower marginal utility. So the consumer is willing to pay less for extra units.

This creates a negative relationship between price and quantity demanded. The demand curve usually slopes downward from left to right.

Ordinal Utility and Indifference Curve

Ordinal utility analysis studies consumer preference through ranking. It does not measure satisfaction in numbers.

An indifference curve class 12 question usually tests meaning, slope, MRS and properties. The curve joins bundles that give equal satisfaction.

Indifference curve

An indifference curve joins all points representing bundles among which the consumer is indifferent. Each point on the same curve gives the same satisfaction.

For example, a consumer may be equally satisfied with different combinations of bananas and mangoes. These combinations lie on one indifference curve.

Marginal Rate of Substitution

Marginal Rate of Substitution shows how much of one good a consumer sacrifices for one more unit of another good. Total satisfaction remains unchanged.

Formula:

MRS = |∆Y/∆X|

If a consumer sacrifices 3 mangoes for 1 banana, MRS is 3:1.

Law of diminishing MRS

The law of diminishing MRS states that the consumer sacrifices less of one good for each additional unit of another good. This happens as the quantity of the first good increases.

If bananas increase, the marginal utility of bananas falls. The consumer then sacrifices fewer mangoes for each extra banana.

Properties of Indifference Curves

Indifference curves show preference patterns in ordinal utility analysis. Their shape follows monotonic preferences and diminishing MRS.

Theory of consumer behaviour class 12 notes often test three properties. These are downward slope, higher satisfaction on higher IC and non-intersection.

Indifference curves slope downward

An indifference curve slopes downward from left to right. More of one good requires less of the other good to keep satisfaction constant.

If the consumer gets more bananas without giving up mangoes, satisfaction rises. The consumer then moves to a higher indifference curve.

Higher indifference curve gives higher utility

A higher indifference curve represents a higher level of satisfaction. It contains bundles with more of at least one good and no less of the other.

This follows monotonic preferences. A consumer prefers more goods when the other good is not reduced.

Two indifference curves never intersect

Two indifference curves cannot intersect because intersection gives conflicting satisfaction rankings. One bundle cannot belong to two different satisfaction levels.

If two curves intersect, the consumer would treat unequal bundles as equal. This contradicts monotonic preferences.

Budget Set and Budget Line

Budget set is the collection of bundles a consumer can buy with income at given prices. Budget line shows bundles that cost the entire income.

Budget line class 12 microeconomics questions usually ask equation, slope, intercepts and shifts. The NCERT chapter uses bananas and mangoes to explain this.

Budget constraint

The budget constraint is:

p1x1 + p2x2 ≤ M

Where:

p1 = price of good 1

p2 = price of good 2

x1 = quantity of good 1

x2 = quantity of good 2

M = consumer income

Budget line equation

The budget line includes bundles that cost exactly the consumer’s income.

Formula:

p1x1 + p2x2 = M

Rearranged form:

x2 = M/p2 − (p1/p2)x1

The slope of the budget line is:

−p1/p2

Meaning of budget line slope

The slope shows the rate at which the consumer can substitute one good for another in the market. It depends on the price ratio.

If the consumer buys one more banana, she gives up p1/p2 units of mangoes. This happens when the entire budget is already spent.

Changes in the Budget Line

The budget line changes when income or prices change. Income changes shift the line, while price changes rotate it.

Class 12 micro economics chapter 2 notes often include numerical questions on this topic. The answer works best when intercepts and slope are mentioned.

Change in income

If income increases and prices remain unchanged, the budget line shifts outward. The slope remains the same.

If income falls and prices remain unchanged, the budget line shifts inward. Both intercepts decrease.

Change in price of one good

If the price of good 1 rises, the budget line becomes steeper. The horizontal intercept falls.

If the price of good 1 falls, the budget line becomes flatter. The horizontal intercept rises.

When both prices and income double

If both prices and income double, the budget set remains unchanged. The consumer can buy the same bundles as before.

This is because purchasing power remains the same. The budget line stays in the same position.

Consumer’s Optimum

A rational consumer chooses the most preferred bundle from the budget set. This bundle gives maximum satisfaction within income and prices.

Consumer behaviour class 12 revision notes need this section because optimum connects preferences and affordability. NCERT places the optimum where the budget line touches an indifference curve.

Meaning of consumer optimum

Consumer optimum is the best affordable bundle. It lies on the highest possible indifference curve within the budget set.

A point below the budget line is not optimum. The consumer can move to another affordable bundle with more of at least one good.

Tangency condition

The optimum bundle is usually located where the budget line is tangent to an indifference curve.

At this point:

MRS = p1/p2

This means the consumer’s willingness to substitute equals the market’s substitution rate.

Why tangency matters

MRS shows how much the consumer is willing to give up. Price ratio shows how much the consumer has to give up in the market.

If MRS is greater than the price ratio, the consumer can improve satisfaction by changing the bundle. At optimum, both rates are equal.

Demand Function and Demand Curve

A demand function shows the relation between price and quantity demanded. It assumes other factors remain unchanged.

In CBSE Class 12 Micro Economics Chapter 2 Theory of Consumer Behaviour, demand comes after consumer optimum. The chosen quantity changes when price, income or preferences change.

Demand function

The demand function can be written as:

X = f(P)

Where:

X = quantity demanded

P = price of the good

Demand depends on price when income, related goods’ prices and preferences remain constant.

Linear demand

A linear demand curve can be written as:

d(p) = a − bp

Where:

a = intercept

−b = slope

p = price

At price 0, demand is a. At price a/b, demand becomes 0.

Substitution effect and income effect

When a good becomes cheaper, the consumer may substitute it for another good. This is the substitution effect.

A fall in price also increases purchasing power. This is the income effect.

Normal Goods, Inferior Goods and Related Goods

Demand changes when income or related goods’ prices change. The direction depends on the type of good.

NCERT explains normal goods, inferior goods, substitutes and complements in the demand section. These terms help answer shift-based questions.

Normal goods

A normal good has demand that moves in the same direction as income. When income rises, demand rises.

When income falls, demand falls. Most commonly consumed goods behave as normal goods at usual income levels.

Inferior goods

An inferior good has demand that moves opposite to income. When income rises, demand falls.

Low-quality cereals are an NCERT example. A consumer may shift to better-quality food after income increases.

Substitutes

Substitutes are goods that can be used in place of each other. Tea and coffee are common examples.

If the price of coffee rises, demand for tea may rise. Demand for a good usually moves in the same direction as the price of its substitute.

Complements

Complements are goods consumed together. Tea and sugar are common examples.

If the price of sugar rises, demand for tea may fall. Demand for a good moves opposite to the price of its complement.

Movement and Shift in Demand Curve

A movement along the demand curve happens due to a change in the good’s own price. A shift happens due to other factors.

This distinction is important in demand questions. Price changes and non-price changes must be written separately.

Movement along demand curve

When the price of the same good changes, there is movement along the demand curve. A fall in price causes expansion of demand.

A rise in price causes contraction of demand. Income, preferences and related goods’ prices remain unchanged.

Rightward shift

A rightward shift means demand increases at each price. This may happen due to higher income for normal goods.

It may also happen when the price of a substitute rises. Favourable preference change can also shift demand rightward.

Leftward shift

A leftward shift means demand decreases at each price. This may happen due to lower income for normal goods.

It may also happen when the price of a complement rises. Unfavourable preference change can shift demand leftward.

Market Demand

Market demand is the total demand of all consumers at a particular price. It is found by adding individual demand at each price.

The market demand curve is obtained through horizontal summation. This means quantities are added at the same price.

Individual demand

Individual demand shows how much one consumer buys at each price. It depends on that consumer’s income and preferences.

Different consumers may demand different quantities at the same price. Their demand curves may have different shapes.

Market demand curve

The market demand curve shows total market quantity demanded at each price. It adds all individual demands.

If consumer 1 demands q1 and consumer 2 demands q2 at price p, then:

Market demand = q1 + q2

Horizontal summation

Horizontal summation adds quantities, not prices. Each consumer’s demand is added at the same market price.

This gives the market demand curve. It represents all buyers together.

Price Elasticity of Demand

Price elasticity of demand measures how responsive demand is to a change in price. It compares percentage change in demand with percentage change in price.

Price elasticity of demand class 12 questions often ask formula, types and expenditure effect. The answer should mention absolute value where needed.

Formula of price elasticity

Formula:

eD = Percentage change in demand / Percentage change in price

Or:

eD = (∆Q/Q) × (P/∆P)

Where:

∆Q = change in quantity demanded

∆P = change in price

Q = original quantity

P = original price

Elastic demand

Demand is elastic when percentage change in quantity demanded is greater than percentage change in price.

In this case:

|eD| > 1

Luxury goods often have elastic demand. Their demand responds strongly to price changes.

Inelastic demand

Demand is inelastic when percentage change in quantity demanded is less than percentage change in price.

In this case:

|eD| < 1

Necessities often have inelastic demand. Their demand changes less with price.

Unitary elastic demand

Demand is unitary elastic when percentage change in demand equals percentage change in price.

In this case:

|eD| = 1

Total expenditure remains unchanged when price changes.

Elasticity on Demand Curves and Expenditure

Elasticity changes along a linear demand curve. It can also remain constant on special demand curves.

The NCERT chapter connects elasticity with expenditure. This helps students answer price rise and revenue-style questions.

Elasticity along a linear demand curve

For a linear demand curve:

q = a − bp

Elasticity is:

eD = −bp/(a − bp)

At the midpoint, elasticity is 1. Above the midpoint, elasticity is greater than 1.

Below the midpoint, elasticity is less than 1. At the quantity-axis intercept, elasticity is 0.

Constant elasticity demand curves

A vertical demand curve is perfectly inelastic. Its elasticity is 0 at all points.

A horizontal demand curve is perfectly elastic. Its elasticity is infinity at all points.

A rectangular hyperbola has unitary elasticity. Total expenditure remains constant along the curve.

Elasticity and expenditure

If demand is elastic, price and expenditure move in opposite directions. A price rise reduces expenditure.

If demand is inelastic, price and expenditure move in the same direction. A price rise increases expenditure.

If demand is unitary elastic, expenditure remains unchanged. Percentage change in quantity equals percentage change in price.

Important Formulas in Theory of Consumer Behaviour

The main formulas in CBSE Class 12 Micro Economics Chapter 2 Theory of Consumer Behaviour connect utility, budget, demand and elasticity. These formulas support numerical and diagram-based questions.

More formulas:

1. TUn = MU1 + MU2 + ... + MUn
2. MRS = |∆Y/∆X|
3. p1x1 + p2x2 ≤ M
4. x2 = M/p2 − (p1/p2)x1
5. Slope of budget line = −p1/p2
6. MRS = p1/p2
7. X = f(P)
8. d(p) = a − bp
9. eD = (∆Q/Q) × (P/∆P)
10. eD = −bp/(a − bp)

Important Terms in Theory of Consumer Behaviour

Theory of Consumer Behaviour uses terms from utility, preferences, budget and demand. These terms help students answer one-mark and short-answer questions in CBSE Class 12 Micro Economics Chapter 2.

Utility

Utility is the want-satisfying capacity of a commodity.

Total utility

Total utility is total satisfaction from consuming a given quantity.

Marginal utility

Marginal utility is the change in total utility due to one additional unit.

Indifference curve

An indifference curve joins bundles that give equal satisfaction.

Budget set

Budget set is the collection of all affordable bundles.

Budget line

Budget line shows bundles that cost the consumer’s entire income.

Consumer optimum

Consumer optimum is the most preferred affordable bundle.

Demand

Demand is the quantity a consumer is willing and able to buy.

Price elasticity of demand

Price elasticity of demand measures responsiveness of demand to price change.

NCERT-Style Questions from Theory of Consumer Behaviour

In CBSE Class 12 Micro Economics Chapter 2 Theory of Consumer Behaviour, NCERT-style questions usually test budget line, indifference curve, demand and elasticity. Strong answers use definitions, formulas and one direct reason.

Q1. What is the budget set of a consumer?

The budget set is the collection of all bundles a consumer can buy with income at given prices.

Explanation:

If the consumer’s income is M and prices are p1 and p2, any affordable bundle satisfies p1x1 + p2x2 ≤ M.

Formula:

p1x1 + p2x2 ≤ M

Q2. Why is the budget line downward sloping?

The budget line is downward sloping because buying more of one good requires giving up some of the other good.

Explanation:

Income is fixed, and both goods have positive prices. More spending on one good leaves less income for the other.

Formula:

Slope = −p1/p2

Q3. What is monotonic preference?

Monotonic preference means a consumer prefers a bundle with more of at least one good and no less of the other.

Explanation:

If bundle A has more bananas and the same mangoes than bundle B, A is preferred. This explains why higher indifference curves give higher satisfaction.

Fact:

Monotonicity makes indifference curves downward sloping.

Q4. What is the consumer’s optimum condition?

The consumer’s optimum condition is MRS = p1/p2.

Explanation:

At this point, the budget line is tangent to an indifference curve. The consumer’s willingness to substitute equals the market price ratio.

Fact:

The optimum bundle lies on the budget line.

Q5. What is price elasticity of demand?

Price elasticity of demand measures the percentage change in demand due to percentage change in price.

Formula:

eD = %∆Q / %∆P

Explanation:

If quantity changes more than price, demand is elastic. If quantity changes less than price, demand is inelastic.

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