Read the passage carefully and answer the following questions.
There are mainly four series of the transition metals, 3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La and Hf to Hg) and 6d series which has Ac and elements from Rf to Cn. The two series of the inner transition metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as lanthanoids and actinoids respectively. Their chemical properties are transitional between those of s and p-block elements. The transition metals (with the exception of Zn, Cd and Hg) are very hard and have low volatility. Their melting and boiling points are high. Transition metals have incomplete d subshell either in neutral atom or in their ions. With partly filled d orbitals these elements exhibit certain characteristic properties such as display of a variety of oxidation states, formation of coloured ions and entering into complex formation with a variety of ligands. The transition metals and their compounds are known for their catalytic activity.
Which of the following is not regarded as transition metal?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Mercury (Hg)
According to IUPAC, transition metals are metals that have an incomplete d subshell either in the neutral atom or in their ions. Zinc, cadmium and mercury (group 12) have the configuration \( (n-1)d^{10}\,ns^{2} \): the d subshell is full in the atom and stays full in their common ions.
\( \displaystyle \mathrm{Hg\ (Z = 80):\ [Xe]\,4f^{14}\,5d^{10}\,6s^{2}} \)
\( \displaystyle \mathrm{Hg^{2+}:\ [Xe]\,4f^{14}\,5d^{10}} \)
Since mercury never has a partly filled d subshell, it is not regarded as a transition metal, although it is placed in the d-block.
Option (1) Mercury (Hg) — Not regarded as a transition metal. Its 5d subshell is full in the atom and in \( \ce{Hg^2+} \).
Option (2) Silver (Ag) — A transition metal. Ag (Z = 47) is \( \mathrm{[Kr]\,4d^{10}\,5s^{1}} \), but in the +2 state, as in \( \ce{AgF2} \), it is \( \mathrm{4d^{9}} \), an incomplete d subshell.
Option (3) Technetium (Tc) — A transition metal. Tc (Z = 43), in group 7, has a partly filled 4d subshell in the atom itself.
Option (4) Scandium (Sc) — A transition metal. Sc (Z = 21) is \( \mathrm{[Ar]\,3d^{1}\,4s^{2}} \); its single 3d electron makes the d subshell incomplete.
NCERT (2026-27 edition):
Electronic Configurations of the d-Block Elements – …
