When a fall in price of a commodity reduces total expenditure and a rise in price increases it, price elasticity of demand will be :

1. The Law of Demand and Demand Schedules (basic)

Welcome to your first step in mastering Demand Theory! At its heart, the Law of Demand captures a simple, intuitive truth about how we behave as consumers: when the price of a product goes up, we usually buy less of it. Formally, it states that there is a negative (inverse) relationship between the price of a commodity and the quantity demanded, provided all other factors remain constant. This condition of "other things being equal" is known as Ceteris Paribus. As noted in Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.24, if the price of a good like bananas drops, your purchasing power effectively increases, allowing you to buy more—this is known as the income effect.

To visualize this logic, economists use two primary tools: the Demand Schedule and the Demand Curve. A demand schedule is simply a table that lists the specific quantity of a good a person is willing to buy at various price points. For instance, if bananas cost ₹5, you might buy 15; but if the price rises to ₹7, you might only buy 12 Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.28. When we plot these numbers on a graph—with Price on the vertical axis and Quantity on the horizontal axis—we get a downward-sloping demand curve. This slope is the visual proof of the law: as we move down the price axis, we move further right on the quantity axis Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.10.

But why does this happen? Beyond the income effect mentioned earlier, the law is also rooted in the concept of Diminishing Marginal Utility. This suggests that as you consume more of a good, the extra satisfaction (utility) you get from each additional unit decreases. Therefore, you are only willing to buy more units if the price drops to match that lower level of additional satisfaction. Together, these factors ensure that the relationship between price and demand remains fundamentally opposite for most goods in our economy.

Sources: Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.10; Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.24; Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.28

2. Movement vs. Shifts in the Demand Curve (basic)

Hello there! Now that we understand what a demand curve looks like, we need to master a distinction that often trips up even the most seasoned aspirants: the difference between Movement along the curve and a Shift of the curve. Think of it this way—one is walking up and down a ladder (Movement), while the other is picking up the whole ladder and moving it to a different wall (Shift).

A Movement occurs when the price of the good itself changes. If the price falls, we move down the curve to a higher quantity; this is called an Extension or Expansion of demand. If the price rises, we move up the curve to a lower quantity, known as a Contraction of demand. Throughout this process, the demand curve itself stays exactly where it is because we assume everything else—like your income or your tastes—remains constant (a concept economists call ceteris paribus). This inverse relationship is driven by the substitution effect and income effect Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.23.

On the other hand, a Shift happens when the price of the good stays the same, but some other factor changes. For instance, if your income increases, you might buy more of a product even if its price hasn't budged. This causes the entire demand curve to move to the right (an Increase in Demand). Conversely, if a factor like a change in fashion makes a product less popular, the curve shifts to the left (a Decrease in Demand) Microeconomics (NCERT class XII 2025 ed.), Market Equilibrium, p.83. These shifts are fundamental to understanding how markets reach a new equilibrium Microeconomics (NCERT class XII 2025 ed.), Market Equilibrium, p.79.

Feature	Movement Along the Curve	Shift of the Curve
Primary Cause	Change in the Own Price of the good.	Change in Other Factors (Income, Tastes, etc.).
Visual Result	Sliding along the existing line.	The entire line moves Right or Left.
Terminology	Expansion / Contraction.	Increase / Decrease in Demand.

Sources: Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.23; Microeconomics (NCERT class XII 2025 ed.), Market Equilibrium, p.79; Microeconomics (NCERT class XII 2025 ed.), Market Equilibrium, p.83

3. Exceptions to the Law of Demand (intermediate)

In our previous discussions, we established that the Law of Demand typically dictates an inverse relationship between price and quantity. However, the world of economics is rarely so simple! There are specific scenarios where the demand curve slopes upward—meaning as the price of a good rises, consumers actually buy more of it. These are known as Exceptions to the Law of Demand. To understand why this happens, we must look at the tug-of-war between two forces: the Substitution Effect (replacing a dearer good with a cheaper one) and the Income Effect (how a price change affects your overall purchasing power). The most famous exception involves Giffen Goods. These are highly inferior goods that occupy a large portion of a poor consumer's budget. When the price of a Giffen good rises, the consumer feels significantly 'poorer' because their purchasing power drops. Even though the substitution effect encourages them to look for alternatives, the income effect is so powerful that it forces them to cut back on expensive luxury foods (like meat) and buy even more of the basic staple (like bread or coarse cereals) just to survive. As noted in Microeconomics (NCERT class XII 2025 ed.), Chapter 2, p.24, if the income effect is stronger than the substitution effect, the demand for the good becomes positively related to its price. Another fascinating exception is the Veblen Effect (or Conspicuous Consumption). Unlike Giffen goods, these are luxury items like designer watches or rare diamonds. Here, the high price itself is the attraction because it serves as a status symbol. If the price of a 'prestige' brand drops, it may lose its appeal to the elite, and demand might actually fall. Additionally, during times of speculation or emergencies, consumers might buy more of a good even as prices rise because they fear future shortages or even higher prices in the future. While most goods are 'normal goods' where demand rises with income, these exceptions remind us that consumer behavior is deeply influenced by psychological and social factors Microeconomics (NCERT class XII 2025 ed.), Chapter 2, p.24.

Sources: Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.24

4. The Law of Supply and Market Equilibrium (intermediate)

While our previous discussions focused on the consumer's desire to buy, the Law of Supply introduces us to the producer's perspective. In simple terms, the Law of Supply states that, other things being equal, as the price of a good increases, the quantity that firms are willing to offer for sale also increases. This creates an upward-sloping supply curve. Why? Because higher prices offer higher profit margins, incentivizing existing firms to produce more and new firms to enter the market.

To understand the entire market, we look at the Market Supply Curve. This isn't just a random line; it is the horizontal summation of all individual supply curves. If we have multiple firms in a market, at any given price p, the total market supply is the sum of what Firm 1, Firm 2, and so on, are willing to produce Microeconomics (NCERT class XII 2025 ed.), Chapter 4, p.63. Interestingly, this curve is not static. If the number of firms in the industry increases, the market supply curve shifts to the right, meaning more is available at every price point Microeconomics (NCERT class XII 2025 ed.), Chapter 4, p.64.

The magic happens at the Market Equilibrium. This is the point where the plans of consumers (Demand) and the plans of producers (Supply) perfectly align. Graphically, this is the intersection where the quantity demanded equals the quantity supplied (q₀) at a specific price (p₀) Microeconomics (NCERT class XII 2025 ed.), Chapter 5, p.78. If the price were higher than p₀, there would be a surplus (excess supply), forcing firms to lower prices. If the price were lower, a shortage (excess demand) would drive prices up. Under perfect competition, this equilibrium often settles where the market price equals the minimum Average Cost (min AC) of the firms, ensuring no "super-normal" profits in the long run Microeconomics (NCERT class XII 2025 ed.), Chapter 5, p.81.

Sources: Microeconomics (NCERT class XII 2025 ed.), Chapter 4: The Theory of the Firm under Perfect Competition, p.63-64; Microeconomics (NCERT class XII 2025 ed.), Chapter 5: Market Equilibrium, p.73, 78, 81

5. Introduction to Price Elasticity of Demand (PED) (intermediate)

In our previous steps, we established that price and demand generally move in opposite directions. But as a civil services aspirant, you must ask: by how much does demand react? This is where Price Elasticity of Demand (PED) comes in. It is a precise measure of the responsiveness of the quantity demanded of a good to a change in its price. Formally, it is calculated as the percentage change in demand divided by the percentage change in price Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.28. Crucially, elasticity is a pure number—it does not have units like kilograms or rupees, allowing us to compare the "sensitivity" of completely different goods, like salt and smartphones Microeconomics (NCERT class XII 2025 ed.), The Theory of the Firm under Perfect Competition, p.66.

One of the most practical applications of PED is understanding its relationship with Total Expenditure (TE), which is simply Price × Quantity (P × Q). If you are a policymaker raising taxes on a product, you need to know if the total revenue will rise or fall. This depends entirely on elasticity:

Type of Demand	Price Change	Effect on Total Expenditure
Inelastic (|PED| < 1)	Price Increases (↑)	Expenditure Increases (↑)
Elastic (|PED| > 1)	Price Increases (↑)	Expenditure Decreases (↓)
Unitary (|PED| = 1)	Price Increases (↑)	Expenditure remains Constant (–)

Why do some goods have high elasticity while others don't? The primary driver is the availability of close substitutes. For instance, while the demand for food as a whole is inelastic (you must eat to survive), the demand for a specific brand of pulses is highly elastic. If the price of one brand rises, consumers will quickly switch to a different variety Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.31. Therefore, necessities with no substitutes tend to be inelastic, whereas luxuries or goods with many alternatives are elastic.

Sources: Microeconomics (NCERT class XII 2025 ed.), Theory of Consumer Behaviour, p.28, 31, 34; Microeconomics (NCERT class XII 2025 ed.), The Theory of the Firm under Perfect Competition, p.66

6. The Total Expenditure (Outlay) Method of PED (exam-level)

To understand how consumers react to price changes, we often look at the Total Expenditure (TE), also known as the Outlay Method. Total expenditure is simply the product of the price of a good and the quantity purchased (TE = P × Q). When the price of a good changes, there is a 'tug-of-war' between the price and the quantity: a higher price increases expenditure per unit, but the Law of Demand tells us that the quantity demanded will fall, which tends to decrease total expenditure. The Price Elasticity of Demand (PED) determines which of these two forces wins. As noted in Microeconomics (NCERT class XII 2025 ed.), Chapter 2, p. 33, for small changes in price (∆p) and quantity (∆q), the change in expenditure is approximately q∆p + p∆q.

The relationship between price movements and total expenditure can be categorized into three distinct scenarios:

• Inelastic Demand (PED < 1): In this case, the percentage change in quantity is less than the percentage change in price. Therefore, the price change dominates. If the price rises, total expenditure also rises; if the price falls, total expenditure falls. They move in the same direction.
• Elastic Demand (PED > 1): Here, consumers are highly responsive. The percentage change in quantity is greater than the percentage change in price. If the price rises, the drastic drop in quantity causes total expenditure to fall. If the price falls, the surge in quantity causes total expenditure to rise. They move in opposite directions.
• Unitary Elastic Demand (PED = 1): In this balanced state, the percentage change in quantity exactly offsets the percentage change in price. As a result, total expenditure remains constant regardless of whether the price increases or decreases (Microeconomics (NCERT class XII 2025 ed.), Chapter 2, p. 29).

Change in Price	Elasticity (PED)	Impact on Total Expenditure	Direction of Movement
Increase	Inelastic (< 1)	Increases	Same
Increase	Elastic (> 1)	Decreases	Opposite
Decrease	Unitary (= 1)	Unchanged	No Change

Sources: Microeconomics (NCERT class XII 2025 ed.), Chapter 2: Theory of Consumer Behaviour, p.29; Microeconomics (NCERT class XII 2025 ed.), Chapter 2: Theory of Consumer Behaviour, p.33

7. Solving the Original PYQ (exam-level)

Now that you have mastered the building blocks of consumer behavior, this question tests your ability to apply the Total Expenditure Method of measuring elasticity. Remember, Total Expenditure (TE) is simply the product of Price (P) and Quantity Demanded (Q). The key insight here is the direction of movement between price and expenditure. When price and total expenditure move in the same direction (both falling or both rising), it signals that the consumer's demand is relatively unresponsive to price changes. This is the hallmark of inelastic demand, where the percentage change in quantity is smaller than the percentage change in price, as detailed in Microeconomics (NCERT class XII 2025 ed.).

To arrive at the correct answer, (B) < 1, think like a coach: if a fall in price leads to lower total spending, it means the increase in quantity purchased was too weak to offset the lower price per unit. The "quantity effect" failed to beat the "price effect." Conversely, when the price rises and you end up spending more, it proves you are still buying almost the same amount despite the higher cost. This positive correlation between price and spending is the definitive characteristic of demand with an elasticity of less than one.

UPSC often uses the other options to test your conceptual clarity on the "turning points" of elasticity. Option (A) 1, or unitary elasticity, is a common trap; here, any change in price is exactly offset by a change in quantity, leaving total expenditure unchanged. Option (C) > 1 represents elastic demand, where price and expenditure move in opposite directions because consumers are highly sensitive to price changes. Finally, Option (D) Infinity describes a theoretical extreme where any price increase would drop demand to zero, which does not fit the expenditure trend described in the question.