(a) $$\,\,\,$$ AlH₃ + H^$$-$$ $$ \to $$ AlH$$_4^ - $$

Steric number of AlH₃ is = $${1 \over 2}$$ [3 + 3] = 3

$$\therefore\,\,\,$$ AlH₃ is sp² hybridized.

Steric number of AlH$$_4^ - $$ = $${1 \over 2}$$ [3 + 4 +1] = 4

$$\therefore\,\,\,$$ AlH$$_4^ - $$ is sp³ hybridized.

(b) $$\,\,\,$$ H₂O + H⁺ $$ \to $$ H₃O⁺

Steric no of H₂O = $${1 \over 2}$$ (6+ 2) = 4

$$\therefore\,\,\,\,$$ H₂O s sp³ hybridized.

Steric no of H₃O⁺ = $${1 \over 2}$$ [ 8 + 3 $$-$$1] = 4

$$\therefore\,\,\,$$ H₃O⁺ s also sp³ hybridized.

(c) $$\,\,\,$$ NH₃ + H⁺ $$ \to $$ NH₄⁺

Steric no of NH₃ = $${1 \over 2}$$ [5 + 3] = 4

$$\therefore\,\,\,$$ hybridization of NH₃ is sp³

Steric number of NH₄⁺ = $${1 \over 2}$$ [5 + 4 $$-$$ ] = 4

$$\therefore\,\,\,$$ Hybridization of NH₄⁺ is sp³