In which there is change in the type of hybridization when:

Change in hybridization will take place only when there is change in no. of electrons around the central atom in a molecule.

⇒Combination of ${\mathrm{H}}^{+}$ to N of ${\mathrm{NH}}_3$​ will bring no change in hybridization as H+ has no electrons.

⇒Combination of ${\mathrm{H}}^{-}$ to Al of ${\mathrm{AlH}}_{3 }$​ will bring a change in hybridization as there will be addition of 2 electrons around  $\mathrm{Al}$by ${\mathrm{H}}^{-}$

$\underset{s{p}^2}{{\mathrm{AlH}}_3}⟶\underset{s{p}^3}{{\mathrm{AlH}}_4^{-}}$

⇒$\mathrm{NH}{2}^{-}$ formation from ${\mathrm{NH}}_3$ will take place when ${\mathrm{H}}^{+}$ leaves ${\mathrm{NH}}_3$​ molecule. This will not lead to removal of electrons from N atom. There will be no change in type of hybridization.

The correct option is B.