The correct option is B [Cr(H2O)6]2+,[Fe(H2O)6]2+
Magnetic moment =√n(n+2) BM
where n= number of unpaired electrons
The pair that has the same number of unpaired electrons will have the same magnetic moments.
(a) Cr2+=3d4; 4 unpaired electrons
Co2+=3d7; 3 unpaired electrons
(b) Cr2+=3d4; 4 unpaired electrons
Fe2+=3d6; 4 unpaired electrons
(c) Mn2+=3d5; 5 unpaired electrons
Cr2+=3d4; 4 unpaired electrons
(d) Co2+=3d7; 3 unpaired electrons
Fe2+=3d6; 4 unpaired electrons