MHTCET 13 Apr 2026 Shift 1 Paper

Concept:Ostwald's dilution law explains how the degree of dissociation of a weak electrolyte varies with concentration.Explanation:Consider a weak base $\mathrm{BOH}$ dissociating as:$$\mathrm{BOH} \rightleftharpoons \mathrm{B}^{+} + \mathrm{OH}^{-}$$Let the initial concentration be $C$ and the degree of dissociation be $\alpha$.At equilibrium:$[\mathrm{BOH}] = C(1-\alpha)$$[\mathrm{B}^{+}] = C\alpha$$[\mathrm{OH}^{-}] = C\alpha$The base dissociation constant is written as:$$K_b = \frac{[\mathrm{B}^{+}][\mathrm{OH}^{-}]}{[\mathrm{BOH}]}$$Substituting the equilibrium concentrations:$$K_b = \frac{(C\alpha)(C\alpha)}{C(1-\alpha)} = \frac{C\alpha^2}{1-\alpha}$$For a weak base, $\alpha$ is very small, so $1-\alpha \approx 1$.Hence, $K_b \approx C\alpha^2$.Solving for $\alpha$:$$\alpha = \sqrt{\frac{K_b}{C}}$$At a fixed temperature, $K_b$ is constant for a given weak base.Therefore, $\alpha \propto \frac{1}{\sqrt{C}}$.This shows that the degree of dissociation of a weak base is inversely proportional to the square root of its concentration.Answer:Option B: The degree of dissociation of a weak base is inversely proportional to square root of its concentration.