Esters are organic compounds formed by the reaction of an acid with an alcohol. They are widely known in chemistry for their pleasant, sweet, and often fruity aromas. Because of these properties, many synthetic esters are used extensively in the food and perfume industries to mimic natural fruit scents like banana, pineapple, or apple.

Formic acid is found in red ants (a-2). Lactic acid is found in milk (b-1). Tartaric acid is found in tamarind (c-3). Glutamic acid is found in wheat (d-4). Matching these pairs correctly results in the sequence a-2, b-1, c-3, d-4, which corresponds to option A.

Vinegar is an aqueous solution primarily composed of acetic acid (ethanoic acid), typically at a concentration of 5% to 8% by volume. It is produced through the fermentation of ethanol by acetic acid bacteria. The other acids listed are either strong mineral acids or toxic organic acids not found in food-grade vinegar.

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.