The number of d electrons retained in ${\mathrm{Fe}}^{2+}$ (atomic number 26) ion is

The electronic configuration of Fe is (ls)

$\left(1s{)}^2\right(2s{)}^2\left(2\mathrm{p}{)}^6\right(3s{)}^2\left(3\mathrm{p}{)}^6\right(3\mathrm{d}{)}^6(4s{)}^2$

With the removal of 4s electrons ${\mathrm{Fe}}^{2+}$ + is formed. Hence, 3d orbitals retain 6 electrons