Question

How many d electrons are present in ${\mathrm{Cr}}^{2+}$ion?

Answer 1

Number of d electrons in $\mathit{C}{\mathit{r}}^{\mathbf{+}\mathbf{2}}$ ion

1. The Chromium$\left(\mathrm{Cr}\right)$ has the electronic configuration: $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}4{\mathrm{s}}^{1}3{\mathrm{d}}^5$
2. $\left(\mathrm{Cr}\right)$is in $+2$ oxidation state so it loses two electrons.
3. So, after losing the two electrons, one from $\mathrm{s}$ and one from $\mathrm{d}$ the electronic configuration of Chromium $\left(\mathrm{Cr}\right)$should be$1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^4$.
4. The number of d electrons is going to be$4$.

Therefore, The number of d electrons in ${\mathrm{Cr}}^{2+}$ ion is $4$.