Which atom will have unpaired 3d electrons? Zn, Fe, Ca or Ge

Iron have unpaired 3d electrons.

Explanation:

It can be explained by observing electronic configuration of the given elements.

Zn - 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s². Fe - 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s². Ca - 1s² 2s² 2p⁶ 3s² 3p⁶ 4s². Ge - 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p².

Where, Zn is zinc,

Fe is iron,

Ca is calcium and

Ge is germanium.

3d orbital have 5 sub shells which means it can carry 10 electrons. On observing electronic configuration of Zn, 3d orbital have 10 electrons and hence it is completely filled and no unpaired electrons in 3d orbital. On observing electronic configuration of Fe, 3d orbital have 6 electrons and hence have unpaired electrons (as five electrons will fill five sub shell of d orbital and the 6th electron will enter in first sub shell and get paired and the other 4 sub shell will have only one electron and hence will be unpaired). On observing electronic configuration of Ca it does not have 3d orbital and hence it is out of the case. On observing electronic configuration of Ge 3d orbital is completely filled with 10 electrons and hence is completely paired.

Result: Fe have unpaired 3d electrons.