CBSE Class 12 Microeconomics Chapter 2: Theory of Consumer Behaviour NCERT Solutions

Reviewed by NCERT Help Editorial Team · Updated on 29 Jul 2026

NCERT Solutions PDF Class 12 PDF

This section provides detailed NCERT Solutions for Class 12 Microeconomics, Chapter 2, focusing on the Theory of Consumer Behaviour. It covers fundamental concepts such as the budget set, which represents all possible bundles a consumer can afford with their income and prevailing prices, and the budget line, illustrating combinations of two goods that exhaust the consumer's income. The solutions explain why the budget line slopes downwards due to the trade-off between consuming more of one good and less of another, and how its slope represents the rate of exchange between the two goods. It also includes a practical example with calculations for the budget line equation, maximum consumption of each good, and the slope. These solutions are designed to help students grasp these core microeconomic principles, clarify doubts, and prepare effectively for their examinations by offering step-by-step explanations and clear definitions.

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Quick info

Board	CBSE
Class	Class 12
Subject	Micro Economics
Session	2026
Language	English
Type	NCERT Solutions
Chapter	Chapter 2

Chapter summary

Chapter 2 of NCERT Class 12 Microeconomics, 'Theory of Consumer Behaviour', introduces the foundational concepts of consumer choice. This chapter's solutions focus on defining and explaining the budget set and the budget line, including the mathematical representation and graphical interpretation of the budget line. It elaborates on the downward slope of the budget line and its economic meaning, represented by the price ratio. A practical numerical problem demonstrates how to derive the budget line equation and calculate its slope based on given prices and income, reinforcing theoretical understanding with practical application.

Learning outcomes

Understand the definition and components of a consumer's budget set.
Define and explain the concept of a budget line in economics.
Interpret the graphical representation of the budget line.
Explain the reasons for the downward slope of the budget line.
Calculate the slope of the budget line using given prices.
Determine the maximum quantity of each good a consumer can purchase with their income.
Write the equation of the budget line for two goods.

Topics covered

Paper topics

Budget Set
Budget Line
Consumer Income
Market Prices
Consumption Bundles
Budget Line Equation
Slope of Budget Line
Price Ratio
Rate of Exchange
Theory of Consumer Behaviour

Important topics

Budget Set Definition
Budget Line Definition
Downward Slope of Budget Line
Slope Calculation (-P1/P2)
Budget Line Equation (P1x1 + P2x2 = M)

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Questions and Solutions

1. What do you mean by the budget set of a consumer?

What do you mean by the budget set of a consumer?

Solution: The budget set of a consumer is the collection of all possible bundles of goods that the consumer can afford to purchase given their income and the prevailing market prices of the goods. This includes bundles where the total expenditure is less than or equal to the consumer's income. It represents all the affordable consumption choices available to the consumer.

2. What is a budget line?

What is a budget line?

Solution: A budget line is a graphical representation that shows all the different combinations of two goods that a consumer can purchase when they spend their entire income on those goods, given the market prices. If

x_1

is the quantity of good 1 and

x_2

is the quantity of good 2, with prices

p_1

and

p_2

respectively, and income

M

, the budget line is defined by the equation:

p_1 x_1 + p_2 x_2 = M

. Every point on the budget line signifies a consumption bundle that exactly exhausts the consumer's income.

3. Explain why the budget line is downward sloping.

Explain why the budget line is downward sloping.

Solution: The budget line is downward sloping because a consumer has a limited income. To increase the consumption of one good (say, good 1), the consumer must decrease the consumption of the other good (good 2), as the total expenditure must remain constant and equal to the income. The slope of the budget line, which is

\frac{-p_1}{p_2}

\frac{\Delta x_2}{\Delta x_1}

, indicates the rate at which the consumer can substitute good 2 for good 1 (or vice versa) while staying on the budget line. This rate of substitution is negative, reflecting the inverse relationship between the quantities of the two goods that can be consumed.

4. A consumer wants to consume two goods. The prices of the two goods are Rs. 4 and Rs.5 respectively. The consumer's income is Rs 20.

A consumer wants to consume two goods. The prices of the two goods are Rs. 4 and Rs.5 respectively. The consumer's income is Rs 20.

Write down the equation of the budget line.
How much of good 1 can the consumer consume if she spends her entire income on that good?
How much of good 2 can she consume if she spends her entire income on that good?
What is the slope of the budget line?

Solution:

Given:

Price of good 1 ( $p_1$ ) = Rs 4
Price of good 2 ( $p_2$ ) = Rs 5
Income ( $M$ ) = Rs 20

Equation of the budget line: The general equation for a budget line is $p_1 x_1 + p_2 x_2 = M$ . Substituting the given values, the equation becomes: $4x_1 + 5x_2 = 20$
Maximum consumption of good 1: If the consumer spends her entire income on good 1, the quantity of good 2 consumed will be zero ( $x_2 = 0$ ). Using the budget line equation: $4x_1 + 5(0) = 20$ $\Rightarrow 4x_1 = 20$ $\Rightarrow x_1 = \frac{20}{4} = 5$ . So, the consumer can consume a maximum of 5 units of good 1.
Maximum consumption of good 2: If the consumer spends her entire income on good 2, the quantity of good 1 consumed will be zero ( $x_1 = 0$ ). Using the budget line equation: $4(0) + 5x_2 = 20$ $\Rightarrow 5x_2 = 20$ $\Rightarrow x_2 = \frac{20}{5} = 4$ . So, the consumer can consume a maximum of 4 units of good 2.
Slope of the budget line: The slope of the budget line is given by the ratio of the price of good 1 to the price of good 2, with a negative sign: $Slope = -\frac{p_1}{p_2}$ . Substituting the given prices: $Slope = -\frac{4}{5}$ . This means that to consume one more unit of good 1, the consumer must give up 4/5 units of good 2.

Common mistakes

Confusing the budget set with the budget line.
Incorrectly calculating the slope of the budget line.
Misinterpreting the economic meaning of the budget line's slope.
Errors in setting up the budget line equation with given income and prices.

Revision tips

Clearly distinguish between the budget set and the budget line.
Practice drawing budget lines for different income and price scenarios.
Focus on understanding the economic interpretation of the budget line's slope.
Work through the numerical example to solidify calculation skills.
Review the definitions of key terms like 'budget set' and 'budget line' before exams.

Practice MCQs

Q1. What does the budget set of a consumer represent?

Q2. The budget line shows combinations of two goods that:

Q3. Why does the budget line slope downwards?

Q4. If P1 = Rs. 4, P2 = Rs. 5, and M = Rs. 20, what is the equation of the budget line?

Q5. What is the slope of the budget line when P1 = Rs. 4 and P2 = Rs. 5?

Frequently asked questions

What is a budget set in the context of consumer behaviour?

The budget set refers to all possible combinations of two goods that a consumer can purchase given their income and the prevailing market prices for those goods. It includes bundles that cost less than or equal to the consumer's income.

How is the budget line different from the budget set?

The budget line represents only those combinations of two goods that a consumer can buy by spending their entire income. The budget set includes all these combinations on the budget line, plus all affordable combinations that cost less than the entire income.

Why is the budget line typically downward sloping?

The budget line slopes downwards because a consumer has a fixed income. To afford more of one good, they must give up some quantity of the other good, assuming prices remain constant.

What does the slope of the budget line signify?

The slope of the budget line represents the rate at which a consumer can trade one good for another while keeping their total expenditure constant. It is equal to the ratio of the prices of the two goods (specifically, -P1/P2).

How can I calculate the budget line equation?

The budget line equation is derived by summing the total expenditure on each good and setting it equal to the consumer's income. If x1 and x2 are quantities of good 1 and good 2, and P1 and P2 are their prices, the equation is P1*x1 + P2*x2 = M, where M is the income.

What is the maximum amount of Good 1 a consumer can buy if their entire income is spent on it?

The maximum amount of Good 1 the consumer can buy is their total income (M) divided by the price of Good 1 (P1). This is represented as M/P1.

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