The general formula R-COOH defines a carboxylic acid. The functional group -COOH consists of a carbonyl group (C=O) attached to a hydroxyl group (-OH). This specific arrangement is the defining feature of carboxylic acids, distinguishing them from aldehydes (R-CHO), ketones (R-CO-R'), and esters (R-COOR').

Sodium benzoate is widely used as a food preservative because it inhibits the growth of mold, yeast, and some bacteria in acidic conditions. It is particularly effective in carbonated drinks, fruit juices, and pickles, where it helps extend shelf life by preventing microbial spoilage.

Vinegar is essentially a dilute solution of acetic acid (ethanoic acid). It is produced through the fermentation of ethanol by acetic acid bacteria, a process often derived from sugar sources like cane sugar.

Ethanoic acid, commonly referred to as acetic acid, is the main component of vinegar, excluding water. White vinegar is typically a solution containing 4% to 8% acetic acid produced through the fermentation of ethanol. Other options like lemon or orange juice primarily contain citric acid, while tomatoes contain a mixture of citric and malic acids.

Malic acid is a dicarboxylic acid that is widely distributed in nature and is the primary organic acid responsible for the tart taste in apples. It plays a significant role in the Krebs cycle within biological organisms. Other acids listed, such as nitric or sulphuric acid, are strong mineral acids and are not naturally occurring in fruit in significant concentrations.

Vinegar is essentially a dilute solution of acetic acid (ethanoic acid), typically containing 4-8% acetic acid by volume. It is produced through the fermentation of ethanol by acetic acid bacteria. The characteristic sour taste and pungent smell of vinegar are directly attributed to the presence of acetic acid.

Citric acid is a weak organic acid found naturally in citrus fruits. Among the options provided, lemons are well-known for their high citric acid content, which gives them their characteristic sour taste. While other fruits contain organic acids, the concentration in lemons is significantly higher.

The carboxyl group, represented by the formula -COOH, is the defining functional group of carboxylic acids. It consists of a carbonyl group (C=O) bonded to a hydroxyl group (-OH). Alcohols contain only -OH, aldehydes contain a formyl group (-CHO), and ketones contain a carbonyl group bonded to two carbon atoms.

Citric acid is a weak organic acid naturally occurring in high concentrations in citrus fruits. Lemons are well-known for their high citric acid content, which provides their characteristic sour taste. Tamarind contains tartaric acid, while apples contain malic acid.

When a carboxylic acid is reduced with HI and phosphorous, the carbonyl group is completely reduced, resulting in the formation of an alkane. This is because the strong reducing agent HI converts the acid group into a methyl group, producing an alkane.