What is the common name of the given compound?

Picric acid 

The correct answer is option 2. Picric acid.

The compound 2,4,6-trinitrophenol, commonly known as picric acid, is named as such due to historical reasons rather than its actual acidic properties. Picric acid is an organic compound with the chemical formula \(C_6H_2(NO_2)_3OH\). It is a powerful explosive and was historically used as a yellow dye and as an antiseptic.

Although picric acid does not contain a carboxylic acid group \((-COOH)\), which is characteristic of most compounds referred to as acids, it does have phenolic hydroxyl groups \((-OH)\) that can exhibit weak acidic properties. The phenolic hydroxyl groups can release hydrogen ions (protons) in solution, leading to a slightly acidic behavior. These phenolic hydroxyl groups are responsible for the weakly acidic properties of picric acid, which can react with bases to form salts.

The name "picric acid" likely originated from the Greek word "pikros," meaning bitter, which refers to the compound's bitter taste. Over time, the name "picric acid" has remained in use despite the compound's lack of a carboxylic acid group. It is important to note that while picric acid can exhibit acidic properties, it is not a strong acid like sulfuric acid or hydrochloric acid.