Which one of the following does NOT contain COOH group ?
- A.Citric acid
- B.Lactic acid
- C.Tartaric acid
- D.Ascorbic acid
Correct answer
Explanation
The correct answer is D, Ascorbic acid. Vitamin C has no carboxyl group; its acidity comes from an enol group in its ring.
Ascorbic acid, C6H8O6, is a five-membered lactone ring carrying hydroxyl groups. One of those hydroxyls sits on a carbon-carbon double bond, forming an enol, and it gives up a hydrogen ion easily. That is why the compound is called an acid even though it has no –COOH group. It is found in citrus fruits and amla, and its deficiency causes scurvy. The other three are true carboxylic acids found in everyday foods.
Option A is wrong because citric acid, from lemons and oranges, has three COOH groups. Option B is wrong because lactic acid, found in curd and in tired muscles, has one COOH group along with a hydroxyl group. Option C is wrong because tartaric acid, found in tamarind and grapes and used in baking powder, has two COOH groups.
Exam tip: citric = 3 COOH, tartaric = 2, lactic = 1, ascorbic = none (enol acid).
Practice Questions
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- A.One
- B.Two
- C.Three
- D.Four
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- A.10⁻⁷ cm
- B.10⁻⁶ cm
- C.10⁻⁴ cm
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- A.CₙH₂ₙ₊₂
- B.CₙH₂ₙ₋₂
- C.CₙH₂ₙ₊₁
- D.CₙH₂ₙ₋₁
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- D.Elephantiasis
Show answer
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