The number of d-electrons present in Ni²⁺ ions is __________

Atomic number of Ni is 28 and its electronic configuration is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^{8}4{\mathrm{s}}^2.$ When Ni forms Ni²⁺, then 2 electrons removed from 4s and remaining electronic configuration becomes $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{2}3{\mathrm{d}}^8.$

So, the number of d-electrons in Ni²⁺ is 8.