The 'Spin only’ Magnetic moment for [ Ni ( NH _ 3 ) _ 6 ] ^ 2 +...

In the presence of ligand ${NH}_{3}$, pairing does not occur in ${Ni}^{2 +}$ because pairing of electrons cannot create two vacant d-orbitals. Hence, nickel ion undergoes ${sp}^{3}{d}^{2}$ hybridisation and it has two unpaired electrons.

${Ni}^{2 +} = 3{d}^{8}$

No. of unpaired electron $= 2$

The spin only magnetic moment 

$\mu = \sqrt{n\left(n + 2\right)} = \sqrt{8} = 2 . 82BM$

$= 28 . 2 \times {10}^{- 1}BM$

$x = 28$