Statement I: Most of the compounds of the transition elements are coloured in the solid state and in solution.
Statement II: During a d–d transition, the electrons absorb certain radiation from the visible region of the spectrum.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Statement I and statement II are true and statement II is correct explanation of statement I
Transition metal ions have partly filled d orbitals. Around the ion, the ligands (water molecules in solution, anions in a solid) split these d orbitals into sets of slightly different energy, so a d electron can jump from a lower to a higher d orbital.
Statement I: Most of the compounds of the transition elements are coloured in the solid state and in solution. — True. Formation of coloured ions is a typical property of the transition elements; for example, in aqueous solution \( \ce{Cu^2+} \) (3d9) is blue and \( \ce{Ni^2+} \) (3d8) is green. Ions with no d electron or a full d subshell, such as \( \ce{Sc^3+} \) (3d0) and \( \ce{Zn^2+} \) (3d10), are colourless, which is why the statement says “most”.
Statement II: During a d–d transition, the electrons absorb certain radiation from the visible region of the spectrum. — True. The energy gap between the split d orbitals matches light of a particular frequency, which generally lies in the visible region.
Why Statement II explains Statement I?
When white light falls on the compound, the d–d transition removes one part of the visible light, and the light that is left reaches the eye. The compound therefore shows the complementary colour of the light absorbed.
This absorption is the cause of the colour in Statement I, so Statement II is its correct explanation.
NCERT (2026-27 edition):
4.2 Electronic Configurations of the d-Block Elements – “… 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.”
4.3.10 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. … In aqueous solutions where water molecules are the ligands, the colours of the ions observed are listed in Table 4.8.”
Table 4.8: Colours of Some of the First Row (aquated) Transition Metal Ions
