Demand for a commodity refers to:

The correct answer is option 'D' - the quantity of the commodity demanded at a certain price during any particular period of time.

Explanation:
Demand refers to the quantity of a product or service that consumers are willing and able to purchase at a given price and time. It represents the consumers' desire and ability to buy a particular commodity in the market. The demand for a commodity is determined by various factors such as price, income, tastes and preferences, and the availability of substitutes.

Key Points:
- Quantity Demanded: Demand refers to the quantity demanded of a commodity, which represents the specific amount of the commodity that consumers are willing to buy at a particular price and time.
- Price: The price of a commodity plays a crucial role in determining the demand. Generally, as the price of a commodity decreases, the quantity demanded increases, and vice versa, assuming other factors remain constant.
- Period of Time: Demand is not a static concept but varies over time. It is influenced by factors such as seasons, trends, and economic conditions. For example, the demand for winter coats is typically higher in the winter season compared to other times of the year.
- Quantity Demanded at a Certain Price: Demand is not just about the desire or need for a commodity, but it specifically refers to the quantity of the commodity that consumers are willing to purchase at a particular price. It represents the relationship between price and quantity demanded.
- Demand Curve: The relationship between price and quantity demanded is often represented graphically by a demand curve. The demand curve slopes downward from left to right, indicating that as the price decreases, the quantity demanded increases.

In Conclusion:
Demand for a commodity refers to the specific quantity of the commodity that consumers are willing and able to purchase at a certain price during any particular period of time. It is influenced by factors such as price, income, tastes and preferences, and the availability of substitutes. Understanding demand is essential for businesses and policymakers to make informed decisions regarding pricing, production, and resource allocation.

Bill payable is representative personal a/c