Question

The most acidic compound is:
A. \[{C_6}{H_5}COOH\]
B. \[HCOOH\]
C. \[C{H_3}COOH\]
D. \[C{H_3}C{H_2}COOH\]

Answer 1

Hint: As we can observe, all the compounds given to us have one functional group in common: -COOH. This functional group can be identified as carboxyl group. When a carboxyl group is attached to either an alkyl or an aryl group, then we obtain a compound known as carboxylic acid. The trends in acidity of carboxylic acids are explained below.

Complete Step-by-Step answer:
Hence, from the given options, we can infer that all compounds are carboxylic acids. These carboxylic acids tend to lose the hydrogen atom in the carboxyl group to form a carboxylate ion. These kinds of reactions take place when interacting with metals and alkalis, and this loss of hydrogen atom indicates the acidity of the compound.
These carboxylate ions formed are stabilized by resonance structures. The simplest way to understand carboxyl groups is by understanding that electron withdrawal leads to an increase in the acidity of carboxyl groups. On the other hand, electron donation leads to the decrease of acidity in carboxyl groups.
Hence the carboxylic acids with the maximum number of resonance structures are the most stable, and in turn are the most acidic of all. Also, alkane based carboxylic acids are more stable than aryl carboxylic acids.
Hence, the most acidic compound from the given options is \[C{H_3}C{H_2}COOH\]

Hence, Option D is the correct option.

Note: Electronegative substituents increase acidity by inductive electron withdrawal. As expected, the higher the electronegativity of the substituent the greater the increase in acidity (\[F{\text{ }} > {\text{ }}Cl{\text{ }} > {\text{ }}Br{\text{ }} > {\text{ }}I\] ), and the closer the substituent is to the carboxyl group the greater is its effect.