Unitary elastic demand.

Ans. When the proportionate change in the price of a commodity brings about exactly equal proportionate change in its quantity demanded, the demand is said to be unitary elastic.

The numerical value of unitary elastic demand is one.

For instance if the price of a commodity falls by 25 per cent, its demand also rises by 25 per cent. In the case of perfectly elastic demand, the demand curve is horizontal straight line, parallel to X - axis.