Statement I: Zinc, cadmium and mercury of group 12 are d-block elements but are not regarded as transition metals.
Statement II: Transition metals are metals which have an incomplete d subshell either in the neutral atom or in their ions.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I.
The d-block has elements of groups 3–12, but the name transition metal is used only for those with a partly filled d subshell.
Statement I: Zinc, cadmium and mercury of group 12 are d-block elements but are not regarded as transition metals. — True. They have a full d10 configuration in the ground state and in their common oxidation states (Zn2+, Cd2+, Hg2+).
Statement II: Transition metals are metals which have an incomplete d subshell either in the neutral atom or in their ions. — True. This is the IUPAC definition of transition metals.
Why Statement II explains Statement I? By this definition a transition metal needs an incomplete d subshell in the atom or in an ion. Zinc, cadmium and mercury have a complete d10 subshell in both, so they fail the definition and are not regarded as transition metals.
NCERT (2026-27 edition):
Unit 4 The d- and f-Block Elements – “… Now according to IUPAC, transition metals are defined as metals which have incomplete d subshell either in neutral atom or in their ions. Zinc, cadmium and mercury of group 12 have full d10 configuration in their ground state as well as in their common oxidation states and hence, are not regarded as transition metals.”