Question

A graph of vapour pressure and temperature for three different liquids $\mathrm{X}$,$\mathrm{Y}$ and $\mathrm{Z}$ is shown below:

The following inferences are made:

• A. C
• B. A
• C. B
• D. A and C

Answer 1

The correct option is C

B

1. Vapour pressure is the pressure exerted by vapours when they are in equilibrium with the liquid phase at a given temperature.
2. As the temperature of liquid increases, its vapour pressure also increases.
3. If the intermolecular forces between molecules are strong, the vapour pressure will be low and if the intermolecular forces between molecules are weak, the vapour pressure will be high.
4. It can be observed from the plot given in the question that at the same temperature, the vapour pressure of liquid $X$ is relatively more than the vapour pressure of liquid $Y$ and liquid $Z$.
5. This means that the intermolecular forces in liquid $X$ are weakest among the three liquids.
6. So, the statement given in the first inference that $X$ has higher intermolecular interactions compared to $Y$ is wrong.
7. Also, the statement in the third inference that $Z$ has lower intermolecular interactions compared to $Y$ is wrong because it can be observed from the given graph that $Z$ has the highest value of vapour pressure among the three liquids at the same temperature.
8. So, the intermolecular interactions in $Z$ are highest.
9. Hence, the second inference which states that
10. $\mathbf{X}$ has lower intermolecular interactions compared to $\mathit{Y}$ is correct.
11. So option B is correct.