Out of the following which one has more number of unpaired electrons ?
`Zn,Fe^(2+),Ni^(3+),Cu^(+)`

Explanation

The number of electrons in the outermost shell of given elements are :
`""_(30)Zn: 3d^(10) 4s^(2), ""_(26)Fe^(2+): 3d^(6), ""_(28)Ni^(3+):3d^(7), ""_(29)Cu^(+) : 3d^(10)`
`Fe^(2+)` has four unpaired electrons which is maximum in the given set. Zinc and copper have no unpaired electrons, while nickel has three unpaired electrons.