A substance responsible for the sour taste of unripe orange is

Analyze the question: Unripe oranges taste sour because of an acid. We need to identify which class of organic compounds the acid belongs to.

Explain the concept: Citrus fruits such as oranges, lemons and limes contain organic acids, mainly citric acid and ascorbic acid (vitamin C). Citric acid contains carboxyl (-COOH) groups, so it belongs to the family of carboxylic acids, which are also called alkanoic acids. In unripe fruits the acid content is high, and it falls as the fruit ripens and the sugars increase.

Check each option:

• A. Alkene: a hydrocarbon with a C=C bond. It has no sour taste and is not found in fruit juice.
• B. Alkanol: an alcohol (-OH group). Alcohols are not sour. They taste sharp or burning.
• C. Alkanoic acid: contains -COOH. Acids taste sour, so this is correct.
• D. Alkanoate: an ester (-COO-). Esters are responsible for the sweet, fruity smells of ripe fruits, not sourness.

Answer: The sour taste of unripe orange comes from an alkanoic acid (citric acid).

Tip: Remember "Acids are sour, esters are sweet-smelling." Sour taste points to an acid (alkanoic acid), and a fruity smell points to an ester (alkanoate). Ripening turns the sour acids and starches into sweet sugars and fragrant esters.