JEE Main · 2021 · 25 Feb 2021 · Shift 1 · p-Block Elements

Hydrolysis begins with water attacking the central atom, so it proceeds wherever that atom can accept a lone pair. Boron in $\mathrm{B}{\mathrm{F}}_3$ has a vacant $2p$ orbital and is hydrolysed by water to boric acid and fluoroboric acid. Silicon in $\mathrm{SiC}{\mathrm{l}}_4$ and phosphorus in $\mathrm{PC}{\mathrm{l}}_5$ can expand their coordination through vacant $d$ orbitals, and both are hydrolysed readily, to silicic acid and to phosphorus oxychloride and phosphoric acid. In $\mathrm{S}{\mathrm{F}}_6$ the six fluorine atoms surround sulfur so closely that water cannot reach it, and the S-F bonds are very strong, so it survives even hot water. Only $\mathrm{S}{\mathrm{F}}_6$ resists hydrolysis, so the number of inert halides among the four is 1.