Question

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

• A. $Sc>Y>La$
• B. $Cd<Zn<Hg$
• C. $Pd<Ni<Pt$
• D. Both (a) and (b)

Answer 1

The correct option is D Both (a) and (b)

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.