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 statements is correct?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Due to an increase in nuclear charge, there is an increase in the ionization enthalpy along the transition series from left to right.
Along a transition series the nuclear charge rises by one unit at each step, while the added electron enters the inner (n−1)d subshell. These d electrons shield the outer ns electrons only poorly, so the effective nuclear charge felt by the outer electrons increases. As a result, the ionisation enthalpy increases from left to right, though less steeply than across a period of the s and p-block elements.
Why the other options are incorrect
Option (1) All transition metals have high volatility. — Incorrect. The transition metals have low volatility, because of strong metallic bonding; only Zn, Cd and Hg, with full d subshells, are exceptions.
Option (3) The high melting points of transition metals are attributed to the involvement of fewer number of electrons in the interatomic metallic bonding. — Incorrect. The melting points are high because a greater number of electrons, from the (n−1)d as well as the ns orbitals, take part in metallic bonding.
Option (4) shielding effect of d-electrons is less than that of 4f electrons — Incorrect. It is the other way round: the 4f orbitals are more diffuse, so the shielding by 4f electrons is poorer than that by d electrons. This poor shielding causes the lanthanoid contraction.
NCERT (2026-27 edition):
Ionisation Enthalpies
