Question

Phosphorus has greater tendency for catenation then nitrogen

Answer 1

‘The single N-N bond is weaker than P-P bond because of high interelectronic repulsion of the non-bonding electrons, owing to the small bond length. As a result the catenation tendency is weaker in nitrogen.’

This means that the non-bonding electrons in nitrogen repel the non-bonding electrons in other nitrogen more because of the smaller bond length of N-N bond than P-P bond. And hence the N-N bond is weaker than P-P bond.
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