The change from Mn3+ to Mn2+ results in the half-filled (d5 ) configuration which has extra stability.So, MnF3 has most oxidising tendency.
Hence, MnF3 has the strongest oxidizing ability as it undergoes reduction readily.
Spin only magnetic moment is calculated using the following formula
μ=n(n+2)B.M
μ=4(4+2)=24=4.89=5B.M