Which of the following best describes an elastic demand?

Elastic demand refers to a situation where the quantity demanded of a good or service responds significantly to changes in price. When the demand for a product is elastic, it means that consumers will purchase much more of the product if the price decreases and will purchase much less if the price increases. This sensitivity to price changes is often due to the availability of substitutes, consumer preferences, or the proportion of income that the price represents.

In contrast, the other descriptions do not capture the essence of elastic demand. For example, a situation where price changes have little effect on quantity demanded indicates inelastic demand, where consumers are less responsive to price fluctuations. When demand remains constant regardless of price changes, it suggests perfectly inelastic demand, which is a different concept altogether. Lastly, the availability of substitutes typically impacts demand significantly; products with many substitutes tend to have more elastic demand, as consumers can easily switch to alternatives if prices rise. Thus, option B accurately reflects the behavior of elastic demand.