When elasticity is zero, demand curve is

The correct answer is (2) perfectly inelastic. When the elasticity of demand is zero, it means that there is no change in the quantity demanded of a product, no matter how much the price changes. In other words, consumers are not responsive to changes in price, and they will continue to buy the same amount of the product regardless of its price. This situation is known as "perfectly inelastic" demand, and it is represented by a vertical demand curve, where the quantity demanded remains constant regardless of changes in price. This type of demand usually occurs for products that have no substitutes or are considered necessities, such as life-saving medicines or vital goods like water or electricity. In contrast, a perfectly elastic demand curve would be horizontal, meaning that consumers are highly responsive to price changes and would stop buying the product altogether if the price increased even slightly.