MHTCET 11 Apr 2026 Shift 2 Paper

Concept:Thermal stability of alkaline earth metal carbonates decreases as the size of the metal cation decreases down the group order from $\mathrm{Ba}$ to $\mathrm{Mg}$.Explanation:For alkaline earth metal carbonates, thermal stability increases down the group.The stability order is:$$\mathrm{MgCO}_{3} < \mathrm{CaCO}_{3} < \mathrm{SrCO}_{3} < \mathrm{BaCO}_{3}$$Since $\mathrm{MgCO}_{3}$ is the least stable, it decomposes most easily on heating.The $\mathrm{Mg}^{2+}$ ion is the smallest among the given cations.Its high polarising power distorts the $\mathrm{CO}_{3}^{2-}$ ion strongly.This weakens the $\mathrm{C}-\mathrm{O}$ bonds and lowers the decomposition temperature.The decomposition reaction is:$$\mathrm{MgCO}_{3} \xrightarrow{\Delta} \mathrm{MgO} + \mathrm{CO}_{2}$$Hence, $\mathrm{MgCO}_{3}$ decomposes most readily.Answer:$\mathrm{MgCO}_{3}$ decomposes most easily, so Option A is correct.