Question

Select the incorrect statement(s) about $N_2{F}_4$ and $N_2{H}_4$.
(i) In $N_2{F}_4$, d-orbitals are contracted by electronegative fluorine atoms, but d-orbital contraction is not possible by H-atoms in $N_2{H}_4$.
(ii) The $N-N$ bond energy in $N_2{F}_4$ is more than $N-N$ bond energy in $N_2{H}_4$.
(iii) The $N-N$ bond length in $N_2{F}_4$ is more than that in $N_2{H}_4$.
(iv) The $N-N$ bond length in $N_2{F}_4$ is less than that in $N_2{H}_4$.
Choose the correct code.

• A. I, II and III
• B. I and III
• C. II and IV
• D. II and III

Answer 1

The correct option is B I and III

1) s-character tend to concentrate in orbitals that are directed toward electropositive groups and p-character tends to concentrate in orbitals that are directed toward electronegative groups.
2) It can be explained on the basis of Bent's rule. In $N_2{F}_4$, $N-N$ bond has more s-character, hence, bond length decreases. While in $N_2{H}_4$, $N-N$ bond has less s-character (i.e. more p-character), hence bond length increases.