Nitrogen molecule is N2 where two nitrogen atoms are triply bonded,in other words presence of triple bond makes the nitrogen beand strong and less reactive whereas phosphorus is a P4 molecule where each phosphorus molecule is singly bonded,weak and hence more reactive

Nitrogen exists as gas (N2) in nature. Nitrogen gas is very unreactive due to the presence of strong triple bonds and has a complete octet for both atoms. N2 is commonly used in food packaging (the gas in potato chips) because of this property.Phosphorus, on the other hand, exists as solid (P4) in nature. P4 has bonds with unstable angle strains compared to that of N2. As a proof of this reactivity, P4 burns quickly.