JEE Main · 2026 · 21 Jan 2026 · Shift 2 · Classification of Elements and Periodicity

Across period 3 the atomic size falls, so magnesium is larger than aluminium, and each cation is smaller than its parent atom with the more highly charged ${\mathrm{Al}}^{3+}$ the smallest of all. The correct size order is therefore $\mathrm{Mg}>\mathrm{Al}>{\mathrm{Mg}}^{2+}>{\mathrm{Al}}^{3+}$, not the $\mathrm{Al}>\mathrm{Mg}$ written, so the first statement is false. For electron gain enthalpy, chlorine has the largest magnitude of any element and exceeds bromine, while sulphur exceeds oxygen because the very small oxygen atom suffers strong inter-electronic repulsion on accepting an electron, so the order $\mathrm{Cl}>\mathrm{Br}>\mathrm{S}>\mathrm{O}$ holds and the second statement is true. Only the second statement is true.