Question

Among the following ions which has the highest paramagnetism ?

• A. [Cr(H${}_2$O)${}_6$]${}^{3+}$
• B. [Fe(H${}_2$O)${}_6$]${}^{2+}$
• C. [Cu(H${}_2$O)${}_6$]${}^{2+}$
• D. [Zn(H${}_2$O)${}_6$]${}^{2+}$

Answer 1

The correct option is B [Fe(H${}_2$O)${}_6$]${}^{2+}$

$\left[Cr\right(H_{2}O{)}_6{]}^{3+}$
The oxidation number of Cr is +3
Atomic number = 24
Cr = $\left[Ar\right]3d^{5}4s^1$
$C{r}^{3+}=\left[Ar\right]3d^{3}4s^0$
There are three unpaired electrons.

$\left[Fe\right(H_{2}O{)}_6{]}^{2+}$
The oxidation number of Fe is +2.
Atomic number = 26
Fe = $\left[Ar\right]3d^{6}4s^2$
$F{e}^{2+}=\left[Ar\right]3d^{6}4s^0$
There are four unpaired electrons

$\left[Cu\right(H_{2}O{)}_6{]}^{2+}$
The oxidation number of Cu is +2.
Atomic number = 29
Cu = $\left[Ar\right]3d^{10}4s^1$
$C{u}^{2+}=\left[Ar\right]3d^{9}4s^0$
There is one unpaired electron.

$\left[Zn\right(H_{2}O{)}_6{]}^{2+}$
The oxidation number of Zn is + 2.
Atomic number = 30
Zn = $\left[Ar\right]3d^{10}4s^2$
$Z{n}^{2+}=\left[Ar\right]3d^{10}4s^0$
There are no unpaired electrons.

$\left[Fe\right(H_{2}O{)}_6{]}^{2+}$ has the maximum number of unpaired electrons; therefore, the highest degree of paramagnetism.