Answer:
Arsenic
Step-by-step explanation:
The atom that has the lowest first ionization energy is Arsenic.
The first ionization energy is the energy needed to remove the most loosely bound electron of an atom in the gas phase in the ground state.
Ionization energy generally deals with the measure of the readiness of an atom to lose an electron.
- Generally, down a group from top to bottom, ionization energy decreases because of the increasing atomic radii and increasing shielding /screening effect on the outermost shell electrons hence the electrons are held less tightly to the nucleus.
- So, nitrogen, phosphorous and arsenic belongs to the same group and arsenic will have the least first ionization energy.