Explanation

(d)
The element having unpaired electron is paramagnetic. More the number of unpaired electrons, more will be paramagnetic character.
Mn (25)=$1s^{2},2s^{2},2p^{6},3s^{2},3p^{6},4s^{2},3d^{5}$
$\therefore\$5 unpaired electrons
Fe (26)= $1s^{2},2s^{2},2p^{6},3s^{2},3p^{6},4s^{2},3d^{6}$
$\therefore\$4 unpaired electrons
Ni (28)= $1s^{2},2s^{2},2p^{6},3s^{2},3p^{6},4s^{2},3d^{8}$
$\therefore\$2 unpaired electrons
Cu (29)= $1s^{2},2s^{2},2p^{6},3s^{2},3p^{6},4s^{2},3d^{10}$
$\therefore\$1 unpaired electrons
$\therefore\$Mn has maximum and Cu has least paramagnetic property.