Question

Of the following four reactions, formic and acetic acids differ in which respect
(A) Replacement of hydrogen by sodium
(B) Formation of the ester with an alcohol
(C) Reduction of Fehling solution
(D) Blue litmus reaction

Answer 1

Carboxylic acids are the chemical compounds consisting of $- COOH$ group. Carboxylic acid's nature can be easily detected by the blue litmus test, in which when wet blue litmus paper is kept in contact with acidic compounds like carboxylic compounds, then the blue litmus paper changes to blue.

Complete answer:
Chemical compounds are classified into functional groups based on the groups present in them. Carboxylic acids are compounds consisting of $- COOH$ group. The hydrogen atom present in the $- COOH$ group can be replaced by metals like sodium easily.
Thus, both formic and acetic acids are acids, the replacement of sodium by hydrogen is common.
When carboxylic acids and alcohol react with each other, then ester will be formed and the reaction is known as esterification.
Formic acid has a slight aldehyde character. Thus, it can easily reduce the Fehling solution. Whereas in acetic acid there is no such character. Thus, the reduction of the Fehling solution is not common.
Blue litmus reactions can be common in all acidic compounds.
Thus, option C is the correct one.

Note:
Formic acid is also known as methanoic acid which has the molecular formula of $H - CO - OH$ , which consists of $H - CO$ character, which gives slightly carbonyl character. Due to this reason, formic acid can reduce the Fehling solution. Whereas acetic acid does not have this type of character.