Dimerisation in carboxylic acid is due to

$CH_3COOH + C_2H_5^{18}OH \xrightarrow{Conc. H_2SO_4} (X)$
$CH_3COOH + (CH_3)_3C^{18}OH \xrightarrow{Conc. H_2SO_4} (Y)$
In the above reaction $(X)$ and $(Y)$ are respectively:

The reaction $CH_3COOAg + Br_2 \xrightarrow{CS_2}$ is known as the Hunsdiecker reaction. What is the main product of this reaction?

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.

Write a note on electrophilic substitution reactions in the ring of aromatic carboxylic acids.

Arrange the following acids in decreasing order of acidity:
$(I) CH_3CH_2COOH$
$(II) CH_2 = CH - COOH$
$(III) HC \equiv C - COOH$