Answer - D. 0.25

% Change in Quantity = -0.25

Elasticity = -1

Find out (a) % change in price.

The elasticity is ONE means, the demand is unitary elastic. It otherwise means the percentage change in the price just equals to the percentage change in the quantity demanded.

Therefore, the answer will be D. 0.25

As the price and quantity demanded is inversely related, with a fall in the price the quantity demanded rises being other things remains constant, the answer will be in negative.