In the following reaction: $CH_3COOH \xrightarrow{SOCl_2}$ Product. The structure of the main product is:

Oxalic acid when reduced with zinc and $H_2SO_4$ gives

Which of the following set of compounds react with $NaHCO_3$?

Two statements are given below:
Statement $I:$ The melting point of monocarboxylic acids with an even number of carbon atoms is higher than that of acids with an odd number of carbon atoms immediately below and above it in the series.
Statement $II:$ The solubility of monocarboxylic acids in water decreases with an increase in molar mass.
Choose the most appropriate option.

Explain the following and provide reasons:
$(i)$ Carboxylic acid compounds are acidic in nature.
$(ii)$ Carboxylic acid compounds are more acidic than phenol compounds.

Which of the following is the most acidic substance?