Which of the following statements about d-block elements are NOT corr…

The correct answer is Option (3) → All of their ions are coloured

A transition metal ion is coloured when an electron can be excited from a lower energy d orbital to a higher energy d orbital (a d–d transition) by absorbing visible light. This needs a partly filled d subshell. Ions with d⁰ or d¹⁰ configurations have no possible d–d transition and are colourless.

• Option (1) They show variable oxidation states — A correct statement about d-block elements. Both (n−1)d and ns electrons can be lost, e.g. Mn shows +2 to +7.

• Option (2) They exhibit paramagnetic and diamagnetic properties — A correct statement about d-block elements. Ions with unpaired d electrons are paramagnetic (\( \ce{Fe^3+} \), d⁵); d⁰ and d¹⁰ ions are diamagnetic.

• Option (3) All of their ions are coloured — Not a correct statement about d-block elements. Zn (Z = 30) is [Ar]3d¹⁰4s²; losing the two 4s electrons gives \( \ce{Zn^2+} \): 3d¹⁰, which is colourless. Sc (Z = 21) is [Ar]3d¹4s²; \( \ce{Sc^3+} \) is 3d⁰ and also colourless.

• Option (4) They exhibit catalytic property — A correct statement about d-block elements. For example, \( \ce{V2O5} \) in the contact process and finely divided Fe in Haber’s process.

NCERT (2026-27 edition):
Formation of Coloured Ions – “When an electron from a lower energy d orbital is excited to a higher energy d orbital, the energy of excitation corresponds to the frequency of light absorbed (Unit 5). This frequency generally lies in the visible region. The colour observed corresponds to the complementary colour of the light absorbed. The frequency of the light absorbed is determined by the nature of the ligand.”

Table 4.8: Colours of Some of the First Row (aquated) Transition Metal Ions