The pair in which both the species have same magnetic moment (spin only) is.

In ${\left[Cr{\left(H_{2}O\right)}_6\right]}^{2+}and{\left[Fe{\left(H_{2}O\right)}_6\right]}^{2+}{\text{H}}_{\text{2}}\text{O}$ is a weak field ligand. Hence ,it will not pair up the electrons in metals orbital.
$C{r}^{2+}=\left[3d^{4}4s^0\right]$            
 
$F{e}^{2+}=\left[3d^{6}4s^0\right]$
         
Both have 4 unpaired electrons in d- orbital.
$$\begin{gathered} \mu =\sqrt{n(n+2)}BM \\ \mu =\sqrt{24}BM. \end{gathered}$$

Therefore, both have same magnetic moment (BM).