The total number of fundamental particles in Azide ion is

Azide ion is, ${\mathrm{N}}_3^{-}$ , 

atomic no. of 'N'= 7, mass no. = 14, no. of neutrons=14-7=7

For Azide ion,

no. of electrons=3(7)+1=22,

no. of protons=3(7)=21

no. of neutrons = 3(7)=21

Total no. of fundamental particles=21+21+22=64