Which of the following reactions does not involve change in hybridisation?

1.Protonation at oxygen of CH₂O leads to the formation of ion which is reversible and can lose hydrogen ion back. However no change. 2) Hydride ion addition at carbon of CH₂O leads to formation of methanol with sp3 hybridisation. 3) Dissociation of C - Cl bond forms methyl cation sp2 hybridisation. 4) Hydrogenation of ethane forms ethane, with sp3 hybridisation.