Question

The transition metal that has the lowest ionisation energy is:

• A. Cr
• B. Sc
• C. Cu
• D. Fe

Answer 1

The correct option is B Sc

$Sc:1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{1}4s^2.$

In Sc the lone electron in 3d level $\left(3d^1\right)$ is readily removed (due to stable fulfilled configuration). In Cr, the nuclear charge is greater than in Sc, hence to convert Cr to Cr${}^{+}$, it requires greater energy.

For the same reason, Cu and Fe have higher ionisation energy.

Hence, the correct option is $\text{B}$