Which among the following compounds has highest boiling point?

Which among the following is dicarboxylic acid?

Select the CORRECT increasing order of boiling points of alcohols, amines and carboxylic acids of comparable molar mass from the following.

Methyl propanoate on hydrolysis with dil $$\mathrm{NaOH}$$ forms a salt which on further acidification with conc. $$\mathrm{HCl}$$ forms _________.