${\mathrm{BF}}_3\underset{\mathrm{Ether}}{\overset{{\mathrm{LiAlH}}_4}{\to }} \mathrm{X} \stackrel{\mathrm{NaH}}{\to } \mathrm{Y}.$ Hybridization of Boron in the compound ‘Y’ is

$$\begin{gathered} 4{\mathrm{BF}}_3+3{\mathrm{LiAlH}}_4\to 2{\mathrm{B}}_2{\mathrm{H}}_6+3\mathrm{LiF}+3{\mathrm{AlF}}_3; \\ {\mathrm{B}}_2{\mathrm{H}}_6+2\mathrm{NaH} \to 2\mathrm{Na}\left[{\mathrm{BH}}_4\right] \\ \mathrm{Tetrahedral} --- {\left[{\mathrm{BH}}_4\right]}^{-} ... \mathrm{Hybridization} \mathrm{of} \mathrm{Boron} \mathrm{is} {\mathrm{sp}}^3 \end{gathered}$$