Question

Which of the following(s) represent the correct order of first ionisation energy of d-block elements?

Answer 1

Ionisation energy decrease down the group due to increase in size. Hence, $Sc>Y>La$ is a correct order.

Due to increase in size down the group, Cd has less ionisation energy than Zn but Hg has more ionisation energy than both Cd and Zn due to the lanthanide contraction. Lanthanide contraction will increase nuclear charge due to poor shielding effect of f-orbitals.
Hence, $Cd<Zn<Hg$ is the correct order.

Pt has higher ionisation energy than Pd and Ni due to lanthanide contraction, but Pd has higher ionisation energy than Ni due to the exceptional electronic configuration $\left[Kr\right]4d^{10}$ which gives more stability due to the fully filled d- orbitals. Hence, the correct order will be $Ni<Pd<Pt$.

Thus, option (d) is correct.