Question

Zinc and mercury do not show variable valency like d-block elements because
(a) they are soft
(b) their d-shells are complete
(c) they have only two electrons in the outermost subshell
(d) their d-shells are incomplete

Answer 1

hey buddy❣❣

Your ans. is option (b)

because they both have complete [d10] configuration.. so they are stable already.

Answer 2

Answer: Option (b) is the correct answer.

Explanation:

Atomic number of zinc is 30 and its electronic configuration is $[Ar]4s^{2}3d^{10}. And, atomic number of mercury is 80 and its electronic configuration is [Xe]4f^{14}5d^{10}6s^{2}$.

As we known that d-block elements are the elements which have incompletely  filled d-orbital.

Since, both zinc and mercury have completely filled d-orbital. So, they tend to lose only 2 electrons from their outermost shell. Hence, only show a valency of +2 and no variable valency.

Thus, we can conclude that zinc and mercury do not show variable valency like d-block elements because their d-shells are complete.