Check Statement I

Statement I says:

The $\mathrm{N-N}$ single bond is weaker and longer than that of $\mathrm{P-P}$ single bond.

Compare $\mathrm{N-N}$ and $\mathrm{P-P}$ single bonds:

• Due to the very small size of nitrogen, the lone pairs on adjacent N atoms repel strongly.
• Hence, the $\mathrm{N-N}$ single bond is weaker than expected.
• But bond length depends mainly on atomic size:
  • Nitrogen is smaller than phosphorus.
  • Therefore, $\mathrm{N-N}$ bond is shorter, not longer, than $\mathrm{P-P}$ bond.

So:

• "weaker" = true
• "longer" = false

Since the whole statement says "weaker and longer," Statement I is false.

Check Statement II

Statement II says:

Compounds of group 15 elements in $+3$ oxidation states readily undergo disproportionation reactions.

For group 15 elements, the stability of the $+3$ oxidation state increases down the group due to inert pair effect.

• Heavier elements like Sb and Bi have relatively stable $+3$ state.
• Therefore, compounds in $+3$ oxidation state do not generally readily undergo disproportionation.
• In fact, the trend often emphasized is that $+5$ state becomes less stable down the group, while $+3$ becomes more stable.

Hence Statement II is false as a general statement.

Conclusion

• Statement I = False
• Statement II = False

Therefore, the correct option is:

$\boxed{\text{C}}$

Comparison with stored answer

Stored correct answer: C

My derived answer matches the stored answer.