MHTCET 22 Apr 2025 Shift 2 Paper

Concept:Boiling point elevation depends on the number of solute particles, expressed as $\Delta T_b = i K_b m$.Explanation:Here, $K_b$ is the ebullioscopic constant, which is the same for all solutions since the solvent is identical.Hence, $\Delta T_b \propto i \times m$, where $i$ is the van't Hoff factor and $m$ is the molality.For complete dissociation, the van't Hoff factor for each salt is:$\mathrm{KCl} \rightarrow \mathrm{K^+} + \mathrm{Cl^-}$, so $i = 2$$\mathrm{NaCl} \rightarrow \mathrm{Na^+} + \mathrm{Cl^-}$, so $i = 2$$\mathrm{AlCl_3} \rightarrow \mathrm{Al^{3+}} + 3\mathrm{Cl^-}$, so $i = 4$$\mathrm{MgCl_2} \rightarrow \mathrm{Mg^{2+}} + 2\mathrm{Cl^-}$, so $i = 3$Now compare the effective molality $i \times m$ for each option:Option A: $2 \times 0.2 = 0.4$Option B: $2 \times 0.1 = 0.2$Option C: $4 \times 1.0 = 4.0$Option D: $3 \times 0.05 = 0.15$The smallest product is $0.15$, corresponding to $0.05\,m\,\mathrm{MgCl_2}$.Therefore, it causes the minimum boiling point elevation.Answer:Option D: $0.05\,m\,\mathrm{MgCl_2}$ exhibits minimum boiling point elevation.