Question

Why we cannot write electronic configuration of calcium as 2,8,10 ?

Answer 1

The electronic configuration of Ca is

1s2 , 2s2 2p6 , 3s2 3p6 , 4s2 .

2 , 8 , 8 , 2

P subshell contain only 6 electron in its outer most shell . That is why remaining 2 electron goes on 4s.