Magnetic moment depends upon the number of unpaired electrons : (a) V4+ (Z = 23) : [Ar] 3d1 : 1 unpaired electron (b) Mn4+ (Z = 25) : [Ar] 3d3 : 3 unpaired electrons (c) Fe3+ (Z = 26) : [Ar] 3d5 : 5 unpaired electrons (d) Ni2+ (Z = 28) : [Ar] 3d8 : 2 unpaired electrons Number of unpaired electrons are maximum in Fe3+. Hence, it shows maximum magnetic moment and V4+ shows least magnetic moment because it has minimum number of unpaired electrons. The order of magnetic moment is as: Fe3+ (C) > Mn4+ (B) > Ni2+ (D) > V4+ (A)