The spin-only magnetic moment value of the compound with strongest...

The change from Mn³⁺ to Mn²⁺ results in the half-filled (d⁵ ) configuration which has extra stability.So, MnF₃ has most oxidising tendency.

Hence, ${MnF}_{3}$ has the strongest oxidizing ability as it undergoes reduction readily.

Spin only magnetic moment is calculated using the following formula

$\mu = \sqrt{n\left(n + 2\right)}B . M$

$\mu = \sqrt{4\left(4 + 2\right)} = \sqrt{24} = 4 . 89 = 5B . M$