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.
