Question

N2 molecule is chemically inert while white phosphorus is more reactive. Explain...

Answer 1

N2 molecule involves triple bond so has high bond dissociation enthalpy  . White phosphorous P4 involves single bond formation and it also has huge angular strain as angle is 600 so more reactive  than N2 

Answer 2

Nitrogen exists as a triple bonded nitrogen molecule. The bond dissociation energy is high and therefore a large amount of energy is required for nitrogen to react.
Phosphorous does not form triple bonds due to its large size and forms singly bonded P4 molecules. The molecule being unstable is reactive.