Explanation

According to the periodic trends, Nitrogen (N) has the largest ionization energy among the given atoms: N, P, As, and Sb. 

 Ionization energy generally increases from left to right across a period on the periodic table.

Since Nitrogen is to the left of Phosphorus, Arsenic, and Antimony, it will have the highest ionization energy.

Additionally, within a group, ionization energy decreases down the column.