The electronic configuration of Cl is

 1s², 2s², 2p⁶, 3s², 3p⁵

Na is
1s², 2s², 2p⁶, 3s¹

Cu is
1s², 2s², 2p⁶, 3s², 3p⁶, 3d⁹, 4s²

Co is
1s², 2s², 2p⁶, 3s², 3p⁶, 3d⁷, 4s²

Fe is
1s², 2s², 2p⁶, 3s², 3p⁶, 3d⁶, 4s²

a) Nickel 1s², 2s², 2p⁶, 3s², 3p⁶, 3d⁸, 4s²
b) Aluminium 1s², 2s², 2p⁶, 3s¹, 3p² Aluminium is excited because the 3s subshell is not full while the 3p contains electrons.
c) Element "X" 1s², 2s², 2p⁶, 3s², 3p⁵, 4s² "X" is excited because the 3p subshell is not full while the 4s contains electrons.
d) Element "Z" 1s², 2s², 2p⁶, 3s², 3p⁶, 3d5, 4s¹ "Z" is excited because the 4s subshell is not full while the 3d contains electrons.
e) Element "Y" 1s², 2s², 2p⁶, 3s², 3p¹⁰, 3d², 4s¹ "Y" is excited because the 4s subshell is not full while the 3d contains electrons.

3) Aluminium has the atomic number 13 and a mass number of 27. Write the electronic configuration of the aluminium (Al³⁺) ion.
The aluminium ion has 10 electrons and must therefore have hte electronic configuration shown below.
1s², 2s², 2p⁶

4) Write the electronic configurations of the following ions.
a) Cr²⁺
1s², 2s², 2p⁶, 3s², 3p⁶, 3d², 4s²
b) Fe³⁺
1s², 2s², 2p⁶, 3s², 3p⁶, 3d³, 4s²
c) Zn²⁺
1s², 2s², 2p⁶, 3s², 3p⁶, 3d⁸, 4s²