When percentage change in quantity demanded is equal to percentage change in price then demand ...........

Explanation:

Option (3) is correct.
Explanation:
(a) Perfectly Elastic Demand (Ed = ∞) :
When percentage change in quantity demanded is infinite with a slight rise in the price, then demand for such a commodity is said to be perfectly elastic. In such a situation, demand curve is parallel to X-axis.
(b) Unitary Elastic Demand (Ed = 1) :
When percentage change in quantity demanded is equal to percentage change in price, then demand for such a commodity is said to be unitary elastic. Shape of demand curve is rectangular hyperbola and elasticity at every point on this curve is unity.
(c) Relatively Elastic Demand (Ed > 1) :
When percentage change in price of a commodity causes greater percentage change in quantity demanded then demand is said to be highly elastic.