Which one of the following may lead to a movement along the demand curve of a commodity?

In economic theory, a distinction is made between a 'change in demand' and a 'change in quantity demanded'. A movement along the demand curve occurs exclusively due to a change in the price of the commodity itself [1]. When the price falls, there is a downward movement along the curve known as an expansion or extension of demand; conversely, a price increase leads to an upward movement called a contraction [3]. Other factors, such as changes in the price of related commodities (substitutes or complements), changes in consumer income, and shifts in tastes or preferences, do not cause movement along the curve. Instead, these factors cause the entire demand curve to shift rightward or leftward because they change the quantity demanded at every price level. Therefore, only a change in its own price leads to a movement along the existing demand curve.

Sources

1. [1] Microeconomics (NCERT class XII 2025 ed.) > Chapter 2: Theory of Consumer Behaviour > 2.4.5 Shifts in the Demand Curve > p. 25
2. [3] Microeconomics (NCERT class XII 2025 ed.) > Chapter 5: Market Equilibrium > Simultaneous Shifts of Demand and Supply > p. 79