Solutions

Mole fractions can be calculated as

${n_{C{H_2}C{l_2}}} = {{8.5} \over {8.5}} = 0.1$ and ${n_{CHC{l_3}}} = {{11.9} \over {119.5}} = 0.1$

We know that

${p_{total}} = p_{C{H_2}C{l_2}}^o \times \,{x_{C{H_2}C{l_2}}} + p_{CHC{l_3}}^o \times \,{x_{CHC{l_3}}}$

$ = 415 \times 0.10 + 200 \times 0.1 = 61.5$

Mole fraction of CHCl₃ in vapour form can be calculated as

${p_{total}} = p_{CHC{l_3}}^o \times \,{x_{CHC{l_3}}}$

$61.5 = 200 \times \,{x_{CHC{l_3}}}$

${x_{CHC{l_3}}} = {{61.5} \over {200}} = 0.3075$

Let us assume that degree of dissociation is $\alpha$.

$\matrix{ {M{X_2}} & { \to {M^{2 + }} + } & {2X + } \cr {(1 - \alpha )} & \alpha & {2\alpha } \cr } $

Thus, after dissociation total number of moles formed (n) = 3.

Now, we know degree of dissociation is

$\alpha = {{i - 1} \over {n - 1}} = {{2 - 1} \over {3 - 1}} = 0.50$

In the context of solutions and mixtures, a negative deviation from Raoult's law occurs when the interaction between different molecules (A-B interaction) is stronger than the interaction between similar molecules (A-A and B-B interactions). This is because the molecules prefer to interact with each other rather than themselves, leading to a decrease in the overall vapor pressure compared to what would be expected from Raoult's law.

So, the correct option is :

Option D : A - B interaction is stronger than A - A and B - B interaction

Option A suggests that the change in volume ($\Delta V_{mix}$) and change in entropy ($\Delta S_{mix}$) of the mixture are both greater than zero. This doesn't necessarily indicate a negative deviation from Raoult's law. It's possible for these conditions to be true in both positive and negative deviations or even in ideal solutions. Therefore, this option isn't specifically associated with negative deviations.

Option B suggests that there's no change in the volume of the mixture ($\Delta V_{mix} = 0$) and the change in entropy ($\Delta S_{mix}$) is greater than zero. Again, this doesn't specifically indicate a negative deviation from Raoult's law. The volume change upon mixing can be zero, positive, or negative depending on the nature of the interactions among the molecules.

Raoult's law deviations are primarily dictated by the relative strength of the intermolecular forces among the different components in the mixture. Thus, the change in volume and entropy, while they can be related, do not directly determine whether a solution will show a positive or negative deviation.