ANS:A - 1

The relative volatility of a binary mixture at the azeotropic composition is 1. At the azeotropic composition, the two components in the mixture have the same vapor pressures, which means they behave similarly in terms of volatility. As a result, the relative volatility, which is the ratio of the vapor pressures of the two components, becomes 1, indicating that they have equal tendencies to vaporize. So, the correct answer is: 1.