Elasticity refers to the responsiveness of demand or supply to changes in price or income. It is calculated as the percentage change in quantity demanded or supplied divided by the percentage change in price or income. When we plot the demand curve and the price axis, we can see that the curve has a negative slope, which means that as the price increases, the quantity demanded decreases, and vice versa.

Horizontal demand curve:

A horizontal demand curve is a straight line that is parallel to the x-axis. It means that at any price level, the quantity demanded remains constant. In other words, the demand is perfectly elastic, and consumers are highly responsive to changes in price. This situation is rare in the real world, but it can occur in the case of commodities like salt or water, where there are many substitutes available, and consumers can easily switch to other options.

Value of elasticity:

The value of elasticity in the case of a horizontal demand curve is infinite. This is because the percentage change in quantity demanded is infinite as the price changes from one level to another. For example, if the price of water increases from Rs. 10 to Rs. 11, the quantity demanded will fall to zero, as consumers can switch to other sources of drinking water. Similarly, if the price of salt increases from Rs. 20 to Rs. 21, the quantity demanded will be zero, as consumers can switch to other brands of salt.

Conclusion:

In conclusion, a horizontal demand curve represents a situation where the demand is perfectly elastic, and the value of elasticity is infinite. This means that consumers will completely switch to substitutes if there is any change in price.

Yes..the correct option is C.and the reason for this:-
with the slightest increase or decrease in price, it leads to zero demand.it means the demand of any good greatly effected with its minor change in its price.
Lets take an example of any item:- suppose the price of i phone gets shooted then its buyer started getting now more resisted in buying them.

hope.it helps!!