Q.Give the electronic configuration of Mn$^{2+}$ and Cr$^{3+}$.

Step 1. Manganese (Z = 25): neutral ground-state configuration is $[\text{Ar}]3d^5\,4s^2$.

Step 2. Forming $\text{Mn}^{2+}$ removes 2 electrons. Electrons are always removed from the OUTERMOST subshell (the highest-n orbital) first when ionising a transition metal, so both 4s electrons are removed before any 3d electron: $\text{Mn}^{2+}=[\text{Ar}]3d^5$ (note this is the extra-stable, exactly half-filled $d^5$ arrangement).

Step 3. Chromium (Z = 24): neutral ground-state configuration is the anomalous $[\text{Ar}]3d^5\,4s^1$ (not $3d^4\,4s^2$, per section 2.6.4). …

Start from each atom's neutral ground-state configuration, then remove electrons from th …

• Removing 3d electrons before the 4s electrons are exhausted (electrons are always lost from the outermost shell first for transition metals). …