The number of species from the following in which the central atom uses sp³ hybrid orbitals in its bonding is __________.
NH₃, SO₂, SiO₂, BeCl₂, CO₂, H₂ O, CH₄, BF₃

Solution

Chemistry ma’am · 3 steps

Count sigma bonds plus lone pairs on the centre; four means sp3. Watch SiO₂, it is not like CO₂.

1. Steric number. Add the sigma bonds and the lone pairs on the central atom. A total of 2 means sp, 3 means sp², and 4 means sp³. Pi bonds do not count.
2. Silica is a network. SiO₂ is not a small linear molecule. Silicon does not form stable Si=O double bonds, so each Si bonds to four O atoms by single bonds in a giant 3D network of SiO₄ tetrahedra.

   Species	Sigma bonds	Lone pairs	Hybridisation
   NH₃	3	1	sp³
   SO₂	2	1	sp²
   SiO₂	4	0	sp³
   BeCl₂	2	0	sp
   CO₂	2	0	sp
   H₂O	2	2	sp³
   CH₄	4	0	sp³
   BF₃	3	0	sp²

3. So. The central atom is sp³ in NH₃, SiO₂, H₂O and CH₄, so the answer is 4.

The common slip: 3. Treating SiO₂ as linear like CO₂ makes Si sp and gives 3, not 4.

The idea to keep. Hybridisation comes from sigma bonds plus lone pairs on the central atom, never from the formula's look. For a network solid like SiO₂, count the real bonds around each atom.

Answer from the NTA final answer key. Solution by PrepWiser.