This question is addressing covalent bonds. The strength of a covalent bond such as that formed between two nitrogen atoms or two oxygen atoms is determined or classified in terms of the amount of energy that is required to break them.
Experiments have revealed that double bonds are stronger than single bonds and triple bonds stronger than double bonds. Therefore it would take considerably more energy to break the triple bond between two nitrogen atoms than the double bond between two oxygen atoms.
In reality, it takes 945 kcal/mol to break the nitrogen molecule while for the oxygen molecule it takes 497 klcal/mol to break it.
Therefore since it takes more energy to break the bond in the nitrogen molecule than in the oxygen molecule, then it can be concluded that the triple bond between two nitrogen atoms (forming a nitrogen molecule) is stronger than the double bond between two oxygen atoms (forming an oxygen molecule)
