The pair having the same magnetic moment is:

$\left[\mathrm{A}\mathrm{t}.\mathrm{ }\mathrm{N}\mathrm{o}.\mathrm{ }:\mathrm{C}\mathrm{r}=24,\mathrm{ }\mathrm{M}\mathrm{n}=25,\mathrm{ }\mathrm{F}\mathrm{e}=26,\mathrm{ }\mathrm{C}\mathrm{o}=27\right]$

The compounds having the same number of unpaired electrons will have same magnetic moment.

Magnetic moment $\left(\mu \right) = \sqrt{n\left(n+2\right)}$

where $n$ is the number of unpaired electrons

${\left[\text{C}\text{r}{\left({\text{H}}_2\text{O}\right)}_6\right]}^{+2}$

$\text{C}{\text{r}}^{2+}.(3{\text{d}}^4)$ with weak field ligand so unpaired electrons are 4

So, $\mu = \sqrt{4\left(4+2\right)} = \sqrt{24}$

$\text{F}{\text{e}}^{+2}\left(3{\text{d}}^6\right)$ Weak field ligand so unpaired electrons are 4

$\mu = \sqrt{4\left(4+2\right)} = \sqrt{24}$