Question

Two complexes \(\mathrm{[Cr(H_2O)_6]Cl_3}\) (A) and \(\mathrm{[Cr(NH_3)_6]Cl_3}\) (B) are violet and yellow coloured, respectively. The incorrect statement regarding them is :

• A. \(\Delta_0\) values of (A) and (B) are calculated from the energies of violet and yellow light, respectively
• B. both are paramagnetic with three unpaired electrons
• C. both absorb energies corresponding to their complementrary colors.
• D. \(\Delta_0\) value for (A) is less than that of (B).

Hint:

The colour seen is complementary to the colour absorbed, and \(\Delta_0\) corresponds to the light absorbed, not the light transmitted.

Answer 1

The Correct Option is A

Both complexes contain \(\mathrm{Cr^{3+}}\) (\(d^3\), \(t_{2g}^3\)) with three unpaired electrons, so both are paramagnetic: statement (2) is correct.
A complex shows the colour complementary to the light it absorbs: (A) absorbs yellow-green and appears violet; (B) absorbs violet and appears yellow. Statement (3) is correct.
\(\mathrm{NH_3}\) is a stronger field ligand than \(\mathrm{H_2O}\), so \(\Delta_0(A)\lt\Delta_0(B)\): statement (4) is correct (also (B) absorbs higher-energy light).
\(\Delta_0\) is obtained from the energy of the light absorbed (the complementary colour), not from the energy of the violet/yellow light seen, so statement (1) is incorrect.
Answer: (1) \(\Delta_0\) values of (A) and (B) are calculated from the energies of violet and yellow light, respectively