Pick the choices that determine the general properties of transition elements:
A. Good catalysts.
B. Form coloured complexes.
C. Fixed oxidation state.
D. Form interstitial compounds.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A, B and D only
The typical properties of transition elements come from their partly filled (n−1)d orbitals and from the small energy difference between the (n−1)d and ns orbitals: variable oxidation states, coloured ions, catalytic activity, complex formation, paramagnetism, interstitial compounds and alloys.
(A) Good catalysts. — Correct. Their variable oxidation states and ability to form complexes make them good catalysts, e.g. \( \ce{V2O5} \) in the Contact process and finely divided iron in the Haber process.
(B) Form coloured complexes. — Correct. Visible light excites an electron from a lower to a higher d orbital (d–d transition), so the complexes are coloured, e.g. \( \ce{[Ti(H2O)6]^{3+}} \) is violet.
(C) Fixed oxidation state. — Incorrect. Both (n−1)d and ns electrons can be lost, so transition elements show variable oxidation states; manganese shows every state from +2 to +7.
(D) Form interstitial compounds. — Correct. Small atoms such as H, C and N get trapped in the holes of their crystal lattices, e.g. TiC, \( \ce{Mn4N} \) and \( \ce{Fe3H} \). These compounds are hard and have high melting points.
NCERT (2026-27 edition):
Summary – …
