Step-by-step explanation:
Ionization energy is defined as the energy required to remove the most loosely bound electron from a neutral gaseous atom.
With increase in atomic number there will also occur an increase in atomic size of the atom. As a result, there will be less force of attraction between the nucleus and the valence electrons of the atom.
Hence, it is easy to remove the most loosely bound electron. Therefore, with increase in size there will occur a decrease in the size of atom.
Since, out of the given group 5A elements, arsenic is larger in size and nitrogen is the smallest. Therefore, ionization energy for nitrogen will be the highest.
Thus, we can conclude that nitrogen is the element which has the highest ionization energy.