COMEDK202510 May 2025Morning ShiftChemistryd and f Block ElementsActual
Choose the correct statement.
Options
- AIonic compounds of Sc ³⁺ and Cu ⁺ are coloured because of d - d electronic transitions
- BThe order in which the paramagnetic nature of the 4 cations Cr ²⁺, Mn ²⁺, V ²⁺ and Fe ²⁺ vary is V ²⁺ < Cr ²⁺=
- CThe metal Cobalt has the electronic configuration [ Ar ] 3 ~d ^5 in the +3 oxidation state
- DAs the oxidation number of the transition element increases, the ionic nature decreases and the oxides show ac
Correct answer
D. As the oxidation number of the transition element increases, the ionic nature decreases and the oxides show ac
Step-by-step solution
(1) Incorrect: Sc³⁺ has [Ar]3d^0 and Cu^+ has [Ar]3d¹⁰ . With completely empty or completely filled d -orbitals, d - d transitions are not possible. Their compounds are colourless. (2) Incorrect: Paramagnetism depends on number of unpaired electrons n . V²⁺(3d^3) n=3 , Cr²⁺(3d^4) n=4 , Mn²⁺(3d^5) n=5 , Fe²⁺(3d^6) n=4 Correct order: V²⁺ (3) Incorrect: Co is [Ar]3d^74s^2 . In +3 state ( Co³⁺ ), it loses 2 electrons from 4s and 1 from 3d , giving [Ar]3d^6 , not 3d^5 . (4) Correct: By Fajans' rules, higher oxidation st