The spin only magnetic moment of Hexacyanidomanganate (II) ion is ______ BM.

1.73

The correct answer is option 2. 1.73.

The spin-only magnetic moment of a complex ion can be calculated using the formula:

\(\text{Magnetic moment} = \sqrt{n(n+2)} \)

where \( n \) is the number of unpaired electrons.

For the hexacyanidomanganate(II) ion, \( \text{Mn}^{2+} \) has 5 electrons in its d orbitals. Manganese in the +2 oxidation state (Mn(II)) has \(d^5\) configuration. In this case, the cyanide ligands are strong-field ligands, so it forms a low spin complex, meaning the electrons in d-orbital pairs up. Therefore, there is 1 unpaired electron.

Substituting \( n = 1 \) into the formula:

\(\text{Magnetic moment} = \sqrt{1(1+2)} = \sqrt{3} \approx 1.73 \, \text{BM} \)

Since the options provided don't include 5.92, the closest option is 1.73, so option 1, 1.73 BM, would be the correct choice.