Question

The aqueous solutions of the following salts will be colored in the case of:

• A. $Zn{\left({NO}_3\right)}_2$
• B. $Li{NO}_3$
• C. $Co{\left({NO}_3\right)}_2$
• D. $Cr{Cl}_3$
• E. Potash alum

Answer 1

Answer: (C), (D)

The correct options are
C $Co{\left({NO}_3\right)}_2$
D $Cr{Cl}_3$

${Co}^{2+}$

$\uparrow \downarrow$ $\uparrow \downarrow$ $\uparrow$ $\uparrow$ $\uparrow$

$z=27$

$Co=\left[Ar\right]{3d}^7{4s}^2$

${Co}^{2+}=\left[Ar\right]{3d}^7$

Two unpaired electrons present.

${Cr}^{3+}$:

$z=24$

$Cr=\left[Ar\right]{3d}^5{4s}^1$

${Cr}^{3+}=\left[Ar\right]{3d}^3$

$\uparrow$ $\uparrow$ $\uparrow$

$Co{\left({NO}_3\right)}_2$ and $Cr{Cl}_2$ have unpaired electron; hence, they are colored.

The compounds have $Z{n}^{2+},L{i}^{+},C{o}^{2+}andC{r}^{3+}$ with 0, 0, 2 and 3 unpaired electrons. Hence option C and D are correct. Potash alum is colorless.