An aqueous solution of \( \mathrm{NiCl}_{2} \) was heated with excess sodium cyanide in presence of strong oxidizing age…

An aqueous solution of \( \mathrm{NiCl}_{2} \) was heated with excess sodium cyanide in presence of strong oxidizing agent to from \( \left[\mathrm{Ni}(\mathrm{CN})_{6}\right]^{2-} \). The total change in number of unpaired electrons on metal centre is ___

[JEE Main 2021, 20 Jul (Shift 2)]