Which of the following molecules contains both ionic and covalent bonds?

Which of the following represents the correct order of boiling point?

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

How many lone pairs of electrons are present in a hydroxyl ion?

The formal charges of $N_{(1)}$,$N_{(2)}$,and $O$ atoms in the structure $N_{(1)} = N_{(2)} = O$ are respectively:

Identify the odd-electron molecules among $NO$,$NO_2$,$CO$,and $CO_2$. Explain why.