MHTCET 15 Apr 2026 Shift 2 Paper

Concept:For a positively charged ferric oxide sol, coagulation is caused by negative ions (anions), and their coagulating power follows the Hardy–Schulze rule.Explanation:The Hardy–Schulze rule states that the coagulating power of an ion increases with its valency.The anions present in the given electrolytes are:$\mathrm{KNO}_{3}$ gives $\mathrm{NO}_{3}^{-}$ (valency $1$),$\mathrm{K}_{2}\mathrm{SO}_{4}$ gives $\mathrm{SO}_{4}^{2-}$ (valency $2$),$\mathrm{K}_{3}\mathrm{PO}_{4}$ gives $\mathrm{PO}_{4}^{3-}$ (valency $3$),$\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$ gives $\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}$ (valency $4$).Thus, the coagulating power order is:$$\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-} > \mathrm{PO}_{4}^{3-} > \mathrm{SO}_{4}^{2-} > \mathrm{NO}_{3}^{-}$$Since $\mathrm{NO}_{3}^{-}$ is monovalent, it has the minimum coagulating power.Hence, the electrolyte causing minimum coagulation is $\mathrm{KNO}_{3}$.Answer:Option A: $\mathrm{KNO}_{3}$