${ }_7^{14} \mathrm{~N}^{3-}$ nitrogen has an atomic number of 7 . So, it has 7 proton. To find the number of neutrons, have to substract the atomic number from the atomic mass. So, atomic mass of nitrogen is 14 . Neutron is- $14-7=7$. (A.M) (A.N)
When an ion has a negative charge, the atom has gained electrons, therefore to calculate the total number of present electrons, have to add the amount of extra charge to the atomic number, so, $7+3=10$ electrons.