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

An isostere is

Determine the correct $(T)$ and incorrect $(F)$ statements for the permanganate ion $(MnO_4^-)$:
$(a)$ $MnO_4^-$ contains $\sigma$ bonds.
$(b)$ $MnO_4^-$ contains $\pi$ bonds.
$(c)$ $MnO_4^-$ contains both $\sigma$ and $\pi$ bonds.
$(d)$ $MnO_4^-$ is paramagnetic.

Which of the following is a Lewis acid?

Which of the following has a different number of $p_{\pi}-d_{\pi}$ bonds compared to the other molecules?

The correct order in which the $O-O$ bond length increases in the following is