Answer:
C. Responsiveness of quantity demanded to a percentage change in income.
Explanation:
Income elasticity is defined as the responsiveness of the quantity of a good demanded by an individual as his income changes, all other factors being constant.
Mathematically it is calculated as percentage change in quantity demanded divided by percentage change in income.
Income elasticity is used to find out if a good is a necessity or a luxury good.
The demand for goods that are a necessity does not change with a change in income.
However demand for a luxury good increases as income increases and vice versa
