The value of the slope of a normal demand curve is-

A normal demand curve exhibits a negative slope, reflecting the inverse relationship between the price of a commodity and the quantity demanded [2]. This fundamental economic principle is known as the Law of Demand, which states that as the price of a good decreases, the quantity demanded increases, and vice versa [1]. Graphically, this relationship is represented by a curve that slopes downward from left to right [2]. Mathematically, the slope is negative because the change in quantity relative to the change in price moves in opposite directions. This downward slope is primarily attributed to the law of diminishing marginal utility, which suggests that consumers are willing to pay less for each additional unit of a good [2]. Other contributing factors include the substitution effect and the income effect, both of which lead consumers to purchase more of a good when its price falls [4].

Sources

1. [1] Microeconomics (NCERT class XII 2025 ed.) > Chapter 2: Theory of Consumer Behaviour > Derivation of Demand Curve in the Case of a Single Commodity (Law of Diminishing Marginal Utility) > p. 10
2. [2] Microeconomics (NCERT class XII 2025 ed.) > Chapter 2: Theory of Consumer Behaviour > Derivation of Demand Curve in the Case of a Single Commodity (Law of Diminishing Marginal Utility) > p. 11
3. [3] Microeconomics (NCERT class XII 2025 ed.) > Chapter 2: Theory of Consumer Behaviour > 2.4.2 Deriving a Demand Curve from Indifference Curves and Budget Constraints > p. 23
4. [4] Microeconomics (NCERT class XII 2025 ed.) > Chapter 5: Market Equilibrium > w = MRPL and MRPL = MR × MPL > p. 75