Which one of the following is a correct set?

The bond having the minimum bond energy is

Identify the correct sequence of increasing number of $\pi$-bonds in the structure of the following molecules:
$(I) \ H_2S_2O_6 \ \ \ \ \ \ \ \ \ (II) \ H_2S_2O_3 \ \ \ \ \ \ \ \ \ (III) \ H_2S_2O_5$

Which of the following molecules has an axis of symmetry and a coaxial plane of symmetry?

Which of the following species has no $p\pi - p\pi$ bond but has a bond order equal to that of $O_2$?

The $B-F$ bond dissociation energy in $BF_3$ is $646 \, kJ \, mol^{-1}$,whereas the $C-F$ bond dissociation energy in $CF_4$ is $515 \, kJ \, mol^{-1}$. Which of the following is the correct reason for the $B-F$ bond dissociation energy being higher than the $C-F$ bond dissociation energy?