ANS:B - decreases.

The correct answer is: With an increase in pressure, the relative volatility for a binary system decreases. Explanation:

1. Relative Volatility:
   • Relative volatility is a measure of the difference in vapor pressures of the components in a binary mixture.
   • It is defined as the ratio of the vapor pressure of the more volatile component to that of the less volatile component.
   • Mathematically, relative volatility (𝛼α) is expressed as 𝛼=𝑃𝑣1𝑃𝑣2α=Pv2​Pv1​​, where 𝑃𝑣1Pv1​ and 𝑃𝑣2Pv2​ are the vapor pressures of components 1 and 2, respectively.
2. Effect of Pressure:
   • The vapor pressure of a component increases with increasing temperature. However, the effect of pressure on vapor pressure depends on the specific properties of the components and the mixture.
   • In general, increasing the pressure tends to compress the vapor phase, reducing the difference in vapor pressures between the components.
   • As a result, the relative volatility decreases with increasing pressure. This means that the differences in volatility between the components become smaller, making separation by distillation less efficient.
   • Conversely, decreasing the pressure can increase the relative volatility, enhancing the separation efficiency in distillation processes.
3. Dependence on System:
   • While the general trend is for relative volatility to decrease with increasing pressure, there may be exceptions depending on the specific properties of the components in the binary system.
   • Factors such as molecular size, polarity, and interactions between molecules can influence how pressure affects the vapor pressures and relative volatility of the components.
   • In some cases, increasing pressure may actually increase relative volatility if the vapor pressures of the components respond differently to changes in pressure.

In summary, for most binary systems, an increase in pressure tends to decrease the relative volatility, making separation by distillation less efficient. However, the exact effect may vary depending on the specific properties of the components and the mixture.