Question

Statements that are true of d-and f-block elements are:
1. The colour of $K_{2}C{r}_2{O}_7$ is due to d-d transition.
2. Actinides have larger number of oxidation states than lanthanides.
3. Tripositive ions of $Pr(At.No.=59)$ and $Tm(At.No.=69)$ have the same (green) colour.
4. Actinides have paramagnetic moments less than theoretically predicted values.

• A. 2,3,4
• B. 1,2,3
• C. 2,4
• D. 1,2,4

Answer 1

The correct option is A 2,3,4

In $K_{2}C{r}_2{O}_7$ the color is due to charge transfer and not d-d transition.

Actinides exhibit a larger number of oxidation states than lanthanides because, there is a very small energy gap between 5f, 6d, and 7s orbitals.

$P{r}^{3+}$ has two 4f electrons (both unpaired). $T{m}^{3+}$ has twelve 4f electrons (5 pairs and 2 unpaired). Both $P{r}^{3+}$ and $T{m}^{3+}$, with 2 unpaired electrons each, have the same colour.

5f electrons in actinides are less effectively shielded resulting in quenching of orbital contribution of magnetic moments. So their magnetic moments are less than theoretically predicted values.