Statement(I) :  N-N  single bond is weaker than  P-P single bond

Statement(II) : The lone pairs on Nitrogen atom repel due to small size and shorter bond length

$\stackrel{..}{\mathrm{N}}-\stackrel{..}{\mathrm{N}}$ single bond is weak because the lone pairs are closer to each other due to small size of Nitrogen atoms.

$\stackrel{..}{\mathrm{P}}-\stackrel{..}{\mathrm{P}}$  single bond is relatively stronger due to the optimum size of 'P' atoms.