Question
Which one of the following statements is NOT correct?
NDA
General Ability
General Science
2025
NDA 2025 (Phase 1)
NDA General Ability Question (2025) — Solution
Options
- A. The molecules of soap are sodium or potassium salts of long chain fatty acids
- B. The molecules of soap contain both hydrophobic and hydrophilic ends
- C. Detergents are more effective than soaps in hard water
- D. In micelles the ionic-end of the molecules is towards oil droplet while the other end faces outside
Answer
D. In micelles the ionic-end of the molecules is towards oil droplet while the other end faces outside
Step-by-step solution
Soap molecules are sodium or potassium salts of long chain fatty acids. They consist of two parts: a hydrophobic (water-repelling) hydrocarbon tail and a hydrophilic (water-attracting) ionic head. In a micelle formed around an oil droplet, the hydrophobic hydrocarbon tails point inwards and dissolve in the oil droplet, while the hydrophilic ionic ends point outwards and interact with the surrounding water. Therefore, the statement that the ionic end is towards the oil droplet and the other end faces outside is incorrect. Detergents are more effective than soaps in hard water because they do not form insoluble precipitates (scum) with the calcium and magnesium ions present in hard water. Answer: In micelles the ionic-end of the molecules is towards oil droplet while the other end faces outside
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