Which among the following compounds has the highest boiling point?

Formic acid and acetic acid differ in which of the following?

The decreasing order of acidity of the following benzoic acid derivatives is:

$4$-Pentenoic acid when treated with $I_2$ and $NaHCO_3$ gives:

What is the order of reactivity of the following compounds towards sodalime decarboxylation?
$(i)$ $m$-nitro-phenylacetic acid
(ii) $p$-nitro-phenylacetic acid
(iii) $p$-methoxy-phenylacetic acid
(iv) $p$-methyl-phenylacetic acid

Consider the chemical reaction shown below and identify product $A$.