Question

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Identify the incorrect statement.

NEET 2020

• A. The transition metals and their compounds are known for their catalytic activity due to their ability to adopt multiple oxidation states and to form complexes.
• B. The oxidation states of chromium in $Cr{O}_4^{2-}\text{and}C{r}_2{O}_7^{2-}$ are not the same.
• C. $C{r}^{2+}\left(d^4\right)$ is a stronger reducing agent than $F{e}^{2+}\left(d^6\right)$ in water
• D. Interstitial compounds are those that are formed when small atoms like H. C or N are trapped inside the crystal lattice of metals.

Answer 1

The correct option is B The oxidation states of chromium in $Cr{O}_4^{2-}\text{and}C{r}_2{O}_7^{2-}$ are not the same.

$C{r}^{3+}$ ion has $d^3$ configuration $\left(t_{2g}^3{e}_g^0\right)$ which makes $C{r}^{3+}$ stable by providing crystal field stabilisation energy. Thus, $C{r}^{2+}$ ion can easily change to $C{r}^{3+}$ (i.e. get oxidised) and acts as a strong reducing agent
$Cr{O}_4^{2-}$
Oxidation state of $Cr$
$x+(-8)=-2x=+6$

$C{r}_2{O}_7^{2-}$
Oxidation state of $Cr$
$2x+(-14)=-2x=+6$
Option (c) will be the answer