Suppose an nitrogen atom gains two electrons to become an nitrogen ion. what is its electrical charge?

Losing an electron changes the electrical charge of an atom. If atom "X" loses one electron, it becomes more negative, so it is ". if it loses two electrons, it becomes X 2-. Atoms lose electrons when other atoms steal them away. When an atom has lost or gained an electron, it is called an ion

Assuming initial neutrality (equal number of protons and electrons), when an atom gains electrons, it gains a negative charge. When it loses them, it gains a positive charge. This is due to the proportion of electrons to protons. More protons will cause an atom to have a positive charge, more electrons will cause an atom to have a negative charge.

So when a nitrogen gains two electrons and becomes a nitrogen ion, it will have a negative electrical charge.