Question

Which one of the following reactions involves change from sp² to sp³ hybridisation of the central atom?

• A. CH₄ + 2CI₂ → CH₂CI₂ + 2HCI
• B. NH₃ + H⁺ → NH₄⁺
• C. AICI₃ + CI^- → AICI₄^-
• D. H₂0 + H⁺ → H₃O⁺
• E. PCI₃ + CI₂ → PCI₅

Answer 1

The Correct Option is C

In the reaction \( \text{AlCl}_3 + \text{Cl}^- \rightarrow \text{AlCl}_4^- \), the central atom in \( \text{AlCl}_3 \) is aluminum, which initially has an \( sp^2 \) hybridisation because it forms three bonds with chlorine atoms. When a chloride ion \( \text{Cl}^- \) attacks the aluminum atom, the aluminum atom undergoes a change in hybridisation to \( sp^3 \) to accommodate the additional bond with the chloride ion.
Thus, the reaction that involves a change from \( sp^2 \) to \( sp^3 \) hybridisation of the central atom.

The correct option is (C) : \(AICI_3 + CI^- → AICI_4^-\)

Answer 2

We are looking for the reaction where the central atom undergoes a change in hybridization from sp² to sp³. Let’s analyze the options: 

1. CH₄ + 2Cl₂ → CH₂Cl₂ + 2HCl
   Carbon is sp³ hybridized both before and after → ❌
2. NH₃ + H⁺ → NH₄⁺
   Nitrogen is sp³ before and after (no change in hybridization) → ❌
3. AlCl₃ + Cl^- → AlCl₄^-
   In AlCl₃, Al is sp² (trigonal planar); in AlCl₄^-, Al is sp³ (tetrahedral) → ✅
4. H₂O + H⁺ → H₃O⁺
   Oxygen remains sp³ in both → ❌
5. PCl₃ + Cl₂ → PCl₅
   Phosphorus changes from sp³ to sp³d → not sp² to sp³ → ❌

Correct Answer: AlCl₃ + Cl^- → AlCl₄^-