Q71 (NDA-I/2025) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Applied everyday chemistry Answer Verified

Which one of the following statements is NOT correct?

The molecules of soap are sodium or potassium salts of long chain fatty acids

The molecules of soap contain both hydrophobic and hydrophilic ends

Detergents are more effective than soaps in hard water

In micelles the ionic-end of the molecules is towards oil droplet while the other end faces outside

Result

Your answer: — · Correct: D

Explanation

Statement 4 is incorrect because in a micelle, the hydrophobic hydrocarbon tails (non-ionic ends) are oriented towards the interior to interact with the oil droplet, while the hydrophilic ionic ends face outward to interact with water [5]. Soap molecules are indeed sodium or potassium salts of long-chain carboxylic (fatty) acids [2]. They are amphiphilic, containing both a hydrophobic hydrocarbon tail and a hydrophilic ionic head [4]. Detergents are more effective than soaps in hard water because their charged ends do not form insoluble precipitates (scum) with the calcium and magnesium ions present in hard water, allowing them to remain soluble and active [3]. In contrast, soap reacts with these ions to form insoluble salts, reducing its cleansing efficiency [3]. Therefore, the description of the micelle's orientation in statement 4 is the only false claim.

Sources

[1] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.10 > p. 75
[5] https://www.sciencedirect.com/topics/materials-science/soaps-detergent
[2] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > CH COOH CH CH OH CH C C CH CH H O 3 3 2 3 2 3 2 Acid O (E - + - - - - - + thanoic acid) (Ethanol) (Ester) O > p. 73
[3] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > Activity 4.12 > p. 76

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Which one of the following statements is NOT correct?

Explanation

SIMILAR QUESTIONS

Which one of the following statements about the cleansing action of soap is not true?

Assertion (A) : Soaps do not form lather with water containing salts of calcium and magnesium. Reason (R) : Calcium and magnesium salts of long-chain fatty acids are insoluble in water.

Consider the following statements : 1. Soap cannot be used in acidic water. 2. Ionic part of a soap is —COO~.Na+. 3. Soap dissolves in water faster than detergent. Which of the statements given above is/are correct?

Statement I: Hard water does not give lather with soap. Statement II: Calcium and magnesium salts, present in hard Abater form precipitate with soap.

The reaction that takes place in soap making is called saponification. Basically soap is sodium or potassium salts of