Which of the following electronic configurations has the lowest ionization enthalpy ?
(a) `1s^2 , 2s^2 , 2p^6`, ,(b) `1s^2 , 2s^2 , sp^6`
(c) `1s^2 , 2s^2 , 2p^6 , 3s^2`.

Elements a,b,c and d have the following electronic configurations: a:1s^(2),2s^(2),2p^(6) b:1s^(2),2s^(2),2p^(6),3s^(2),3p^(1) c:1s^(2),2s^(2),2p^(6),3s^(2),3p^(6) d:1s^(2),2s^(2),2s^(1) Which elements among these will belong to the same group of periodic table.

The electronic configuration of the elements A and B are 1s^(2),2s^(2),2p^(6),3s^(2)and1s^(2),2s^(2),2p^(5) respectively . The formula of the ionic compound that can be formed between these elements is