Comprehension:
TRANSITION METALS
All the transition elements display typical metallic properties such as high tensile strength, ductility, malleability, high thermal and electrical conductivity and metallic lustre. With the exceptions of Zn, Cd, Hg and Mn, they have one or more typical metallic structures at normal temperatures.
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. The high melting points of these metals are attributed to the involvement of greater number of electrons from (n–1)d in addition to the ns electrons in the interatomic metallic bonding. In any row the melting points of these metals rise to a maximum at d5 except for anomalous values of Mn and Tc and fall regularly as the atomic number increases.
The maxima at about the middle of each series indicate that one unpaired electron per d orbital is particularly favourable for strong interatomic interaction. In general, greater the number of valence electrons, stronger is the resultant bonding. Since the enthalpy of atomisation is an important factor in determining the standard electrode potential of a metal, metals with very high enthalpy of atomisation (i.e., very high boiling point) tend to be noble in their reactions.
Identify the general electronic configuration of d-block elements?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (n-1)d1–10 ns1–2
In the d-block elements the last electron enters a d orbital of the penultimate shell, (n−1)d, while the outermost shell n holds one or two s electrons. A d subshell can hold up to ten electrons, so the general electronic configuration is:
\( \displaystyle (n-1)d^{1-10}\,ns^{1-2} \)
Examples from the first (3d) series:
Sc (Z = 21): [Ar]3d14s2 (first member)
Cr (Z = 24): [Ar]3d54s1 (half-filled d subshell is extra stable, so only one 4s electron)
Cu (Z = 29): [Ar]3d104s1 (completely filled d subshell is extra stable)
Zn (Z = 30): [Ar]3d104s2 (last member)
Why the other options are incorrect
Option (2) nd1–10 ns1 — Incorrect. The d electrons are in the penultimate shell (n−1), not in the outermost shell n, and the s subshell may hold one or two electrons.
Option (3) (n-1)d1–10 ns0 — Incorrect. An empty outer s subshell is found only in palladium, so it is not the general configuration.
Option (4) (n-1)d1–5 ns1–2 — Incorrect. It covers only the first half of each series; the d subshell continues filling up to d10 (Cu, Zn).
NCERT (2026-27 edition):
Electronic Configurations of the d-Block Elements
