The compound which is inert towards hydrolysis is

In SF₆, the six F atoms shield the S atom and do not allow water molecules to attack on S. Also, F has no vacant d-orbitals, therefore cannot accept the lone pair of electrons from water molecules. Therefore, SF₆ shows no reaction with water, whereas other given molecules react with water.

$$\begin{gathered} {\mathrm{NCl}}_3 + 3{\mathrm{H}}_2\mathrm{O} \to {\mathrm{NH}}_3 + 3\mathrm{HOCl} \\ {\mathrm{B}}_2{\mathrm{H}}_6 +3{\mathrm{H}}_2\mathrm{O} \to 2\mathrm{B}{\left(\mathrm{OH}\right)}_3 + 3{\mathrm{H}}_2 \\ {\mathrm{SF}}_6+{\mathrm{H}}_2\mathrm{O}\to \mathrm{No} \mathrm{reaction} \\ {\mathrm{SiCl}}_4+4{\mathrm{H}}_2\mathrm{O}\to \mathrm{Si}{\left(\mathrm{OH}\right)}_4+4\mathrm{HCl} \end{gathered}$$