MHTCET 15 Apr 2026 Shift 1 Paper

Concept:$\Delta S$ is negative when the randomness or disorder of a system decreases.Explanation:Entropy ($S$) measures the degree of randomness in a system.A negative $\Delta S$ means the final state has lesser disorder than the initial state.In adsorption of a gas on a solid surface, gas molecules that were moving freely in all directions get fixed at specific sites on the solid surface.This restricts their freedom of motion and reduces the randomness of the system.Hence, for adsorption, the change in entropy is negative:$$\Delta S < 0$$Now examine the other options.Dissolving sugar in water: sugar molecules spread uniformly in water, increasing randomness. So, $\Delta S > 0$.$2 \mathrm{NH}_{3}(g) \rightarrow \mathrm{N}_{2}(g) + 3 \mathrm{H}_{2}(g)$: the number of gaseous moles increases from 2 to 4, which increases disorder. So, $\Delta S > 0$.Sublimation of dry ice: solid $\mathrm{CO}_2$ changes directly into gas, causing a large increase in randomness. So, $\Delta S > 0$.Answer:$\Delta S$ is negative for the adsorption of a gas on a solid surface.Therefore, the correct option is Option B: Adsorption of a Gas on a Solid Surface.