Total number of species from the following with central atom utilising sp² hybrid orbitals for bonding is ________.
NH₃, SO₂, SiO₂, BeCl₂, C₂ H₂, C₂ H₄, BCl₃, HCHO, C₆ H₆, BF₃, C₂ H₄ Cl₂

Solution

Chemistry ma’am · 3 steps

For each species, count the sigma bonds and lone pairs on the central atom. A total of 3 means sp2.

1. Steric number. Add the sigma bonds and lone pairs on the central atom. A double or triple bond still counts as one sigma bond. A total of 2 means sp, 3 means sp² and 4 means sp³.
2. Watch two species. SiO₂ is not a small molecule like CO₂. It is a network solid in which each Si is bonded to 4 O atoms, so Si is sp³. C₂H₄Cl₂ is dichloroethane, a saturated compound, so each carbon has 4 sigma bonds.

   Steric number	Hybridisation	Species
   2	sp	BeCl₂, C₂H₂
   3	sp²	SO₂ (2 sigma bonds + 1 lone pair), C₂H₄, BCl₃, HCHO, C₆H₆, BF₃
   4	sp³	NH₃ (3 sigma bonds + 1 lone pair), SiO₂, C₂H₄Cl₂

3. So. Six species use sp² hybrid orbitals: SO₂, C₂H₄, BCl₃, HCHO, C₆H₆ and BF₃. The answer is 6.

The common slip: 7. Reading C₂H₄Cl₂ as an alkene and counting it as sp² gives 7. It is dichloroethane, and both of its carbons are sp³.

The idea to keep. Hybridisation comes from the steric number: sigma bonds plus lone pairs on the central atom. Count the lone pairs, and do not count the pi bonds.

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