[ronit]

Perfectly Elastic :-Elasticity is infinite, when some 'small price reduction raises the demand from zero to infinity. Under such a case consumers will buy all that they can obtain of the commodity at some price. If there is a slight increase in price, they would not buy anything from the particular seller. This type of demand curve is found in perfectly competitive market.

Perfectly inelastic: Elasticity is zero, if there is no change at all in quantity demanded when price changes i.e. when quantity demanded does not respond to a price change.