JEE Main · 2025 · 02 Apr 2025 · Shift 1 · p-Block Elements

Across the first four halogens the covalent radius rises steadily $\mathrm{F}<\mathrm{Cl}<\mathrm{Br}<\mathrm{I}$, the ionic radius rises in the same order $\mathrm{F}{}^{-}<\mathrm{Cl}{}^{-}<\mathrm{Br}{}^{-}<\mathrm{I}{}^{-}$, and the first ionisation energy falls regularly $\mathrm{F}>\mathrm{Cl}>\mathrm{Br}>\mathrm{I}$. The electron affinity alone breaks the trend: chlorine releases more energy on gaining an electron than fluorine does, giving $\mathrm{Cl}>\mathrm{F}>\mathrm{Br}>\mathrm{I}$, because the compact 2p shell of fluorine forces strong repulsion on the added electron. The only property showing irregularity is the electron affinity.