JEE Chemistry 2026 Question with Solution

Given: A mixture of acetone and $CS_2$ at constant temperature.

Find: Which graph represents the plot of partial pressure of $CS_2$ versus its mole fraction.

A mixture of acetone and carbon disulfide ($CS_2$) shows positive deviation from Raoult's law because the intermolecular attractions between acetone-$CS_2$ are weaker than acetone-acetone or **$CS_2$-CS_2$** attractions.$

In a solution showing positive deviation:

• The vapor pressure of each component is higher than that predicted by Raoult's law.
• Therefore, the graph of partial pressure $P_{CS_2}$ against mole fraction $x_{CS_2}$ is not a straight line.
• It is a curve bowed upward.

Positive deviation is often associated with

and

So, the correct graph is the one showing positive deviation for partial pressure, which is Graph 1.

Therefore, the correct option is A.

Given: Acetone and $CS_2$ form a non-ideal solution.

Find: The correct qualitative shape of the $P_{CS_2}$ versus $x_{CS_2}$ graph.

When unlike molecular interactions are weaker than like molecular interactions, molecules escape more easily into the vapour phase. Hence the observed partial pressure becomes greater than the value predicted by Raoult's law.

Thus, instead of following a linear relation,

the actual curve lies above the Raoult's law line and bends upward.

So the graph corresponding to upward deviation is selected.

Therefore, the correct option is A.