Correct orders of first I.P. are -
(i) Li < B < Be < C
(ii) O < N < F
(iii) Be < N < Ne
(i), (ii), (iii)
Down the group ionization potential (ionization enthalpy) decreases with increase in size.
Across a period, ionization potential decreases and then increases at the noble gases.
Elements of group 2(IIA) have I.E more than that of group 13(IIA) as they have completely filled shells. Be > B
Elements of group 15(VA) have more than that of group 16(VIA) as they have half filled subshell. N > O
Inert gas elements have the highest I.P in a given period due to a stable electronic configuration.