KCET 2026 Chemistry Solved Paper

Concept:Colligative properties depend on the number of solute particles, not their nature.Explanation:NaCl dissociates as $\mathrm{NaCl} \rightarrow \mathrm{Na}^{+} + \mathrm{Cl}^{-}$, so its van't Hoff factor is $i \approx 2$.Urea does not dissociate, so $i = 1$.Osmotic pressure is given by $\pi = iCRT$.For equal concentrations, $\pi_{\mathrm{NaCl}} > \pi_{\mathrm{urea}}$.Thus, $0.1\,\mathrm{M}$ NaCl has higher osmotic pressure than $0.1\,\mathrm{M}$ urea, so Option A is false.$2\,\mathrm{ppm}$ is a very dilute concentration, about $2\,\mathrm{mg}$ per litre.$2\,\mathrm{M}$ means $2$ moles per litre, which is far more concentrated.Hence, $2\,\mathrm{ppm} < 2\,\mathrm{M}$, so Option B is false.Boiling point elevation is $\Delta T_b = iK_b m$.Since $i_{\mathrm{NaCl}} \approx 2 > i_{\mathrm{urea}} = 1$, we get $\Delta T_b(\mathrm{NaCl}) > \Delta T_b(\mathrm{urea})$.So $0.02\,\mathrm{M}$ NaCl raises boiling point more than $0.02\,\mathrm{M}$ urea, making Option C false.Salt is non-volatile; adding salt to water lowers its vapour pressure.Therefore, vapour pressure of salt water is less than that of pure water.Answer:Option D is correct: Vapour pressure at 298 K: Salt water < Pure water.