The element with highest ionization potential is :
(A) nitrogen
(B) oxygen
(C) helium
(D) neon

Hint: An attempt to this question can be made by determining the meaning of ionization potential of an element. Now determine the factors that affecting ionization potential of an element. Write the electronic configuration of the elements given in options. Based on this determine the electron that will face the most obstruction while leaving the orbit of the element. With this you can determine the element with the highest ionization potential.

Complete step by step answer:
Ionization energy can be defined as the minimum amount of energy required to remove the most loosely bound electron of an isolated neutral gaseous atom or molecule.
It is observed that the reaction is usually endothermic. This means that energy must be supplied for the reaction to occur. The ionization energy for an atom/ion is directly proportional to the effective nuclear charge for the species under consideration.
It is observed that ionization potential increases from left to right in a period and is highest for noble gases. This is because they have a stable complete octet configuration that requires a lot of energy to overcome the force of attraction.
Thus, the element with highest ionization potential is helium.

Therefore, the correct answer is option (C).

Note: Ionization energy can be alternatively determined using the effective nuclear charge of the element in its ground state configuration. The element or ion having higher effective nuclear energy will have higher ionisation energy.