Answer:
Carbon.
Step-by-step explanation:
Ionization energy may be defined as the amount of energy required to remove the electrons from its outermost shell. Metals have low ionization energy whereas non metals have high ionization energy.
As we go left to right in a period, the ionization energy increase as the non metallic character increases. Li,Be,B, and C are arranged left to right in a period. Hence, the carbon has the highest ionization energy as it belongs to the rightmost in the periodic table.
Thus, the correct answer is carbon.