Question

ionization enthalpy of ne is more than f although ne has bigger size than the f

Answer 1

because ne is in stable state due to fullfill size of its own and f is first member of its group due to this it show anamolus behavior and it has lack of one electron in its our most shell to complete its octet.
hope it will help you.

Answer 2

ionization enthalpy means minimum energy required in losing an electron..
ne has a completely filled octet and it is stable while f is short of one electron and it is not so stable as he is ...
Therefore ne require more energy in losing electron than f ...So ne has more ionization enthalpy than f