Pyramidal Geometry Around Central Atom

Question:
The number of species from the following that have pyramidal geometry around the central atom is ________.

S₂O₃²⁻, SO₄²⁻, SO₃²⁻, S₂O₇²⁻

Correct Answer: 1

Explanation

Let us analyse the geometry around the sulphur atom in each species:

1. SO₄²⁻ (Sulphate ion):
Sulphur is surrounded by four bonding pairs and no lone pair. Geometry → Tetrahedral.

2. SO₃²⁻ (Sulphite ion):
Sulphur has three bonding pairs and one lone pair. Hybridisation → sp³
Geometry → Trigonal pyramidal.

3. S₂O₃²⁻ (Thiosulphate ion):
Central sulphur does not show pyramidal geometry.

4. S₂O₇²⁻ (Pyrosulphate ion):
Each sulphur atom has tetrahedral geometry.

Hence, only one species (SO₃²⁻) shows pyramidal geometry.

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