Correct Answer - d

Magnetic moment `mu_(m) = sqrt(n(n+2))` B.M.

where n = number of unpaired `e^(-)`

(a) `underset(n=0)(._(30)Zn^(2+))rArrunderset(mu_(m)=0)(1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(10))`

(b) `._(28)Ni^(+2)rArr1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d%(8)`

`3d^(8)rArr`

n=2

Hence `rArr mu_(m) = sqrt(n(n+2))`

`mu_(m) = sqrt(2(2+2))=sqrt(8)B.M.`

(c) `._(24)Cr^(+3) = 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(3)`

`3d^(3)rArr`

n=3

`mu_(m)=sqrt(3(3+2))rArrsqrt(15)B.M.`

(d) `._(25)Mn^(+3)=1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(4)`

`3d^(4) rArr`

n=4

`mu_(m) = sqrt(4(4+2))rArrsqrt(24)`B.M.