Question

The number of statement(s) correct from the following for Copper (at. no. 29) is/are ______.

1. Cu(II) complexes are always paramagnetic
2. Cu(I) complexes are generally colourless
3. Cu(I) is easily oxidized
4. In Fehling solution, the active reagent has Cu(I)

Answer 1

Correct Answer: 3

(A) Cu(II) complexes are always paramagnetic as they have one unpaired electron due to d⁹ configuration of Cu(II).
(B) Cu(I) complexes are generally colourless due to d¹⁰ configuration.
(C) Cu(I) is easily oxidised to Cu⁺² in aqueous solution.
\(2Cu^+ → Cu^{+2} + Cu\)
Cu⁺¹ disproportionates to Cu⁺² and Cu
( \(E_{cell}^∘>0\) for this cell reaction in aqueous solution)
In Fehling’s solution, active reagent has Cu(II) which is reduced to Cu(I) on reaction with aldehydes.

Hence, (D) statement is incorrect.

So, the answer is 3.