Identify reductant in following reaction.

$$\mathrm{H}_2 \mathrm{~S}+\mathrm{NO}_2 \rightarrow \mathrm{H}_2 \mathrm{O}+\mathrm{NO}+\mathrm{S}$$

What is the value of critical temperature of water?

Identify the compound from following having lowest boiling point.

Which among the following isomers of $$\mathrm{C}_4 \mathrm{H}_9 \mathrm{OH}$$ has lowest boiling point?