35. What happens to soap molecules when they are added to water?
[RRB Group D (2025 recruitment cycle), Shift 3 — 25 Aug 2026]
(A) The hydrocarbon tail remains in water while the ionic heads project outwards
(B) Soap molecules dissolve randomly without any specific orientation
(C) The ionic heads remain in water while the hydrocarbon tails project outwards
(D) Both the ionic heads and tails remain completely inside water
Answer: (C) The ionic heads remain in water while the hydrocarbon tails project outwards
Explanation: Soap molecules possess an ionic, water-attracting head and a non-polar, water-repelling tail. At a water–air interface, their heads stay in water while tails point away. In micelles formed within water, however, the tails gather inward and the heads face outward.
34. Why does a soap solution appear cloudy?
[RRB Group D (2025 recruitment cycle), Shift 3 — 20 Aug 2026]
(A) Because soap micelles are large enough to scatter light
(B) Because soap molecules dissolve completely
(C) Because hydrocarbons are soluble in water
(D) Because dust remains suspended in water
Answer: (A) Because soap micelles are large enough to scatter light
Explanation: Above a certain concentration, soap molecules aggregate into micelles, which behave as colloidal particles. Their dimensions permit scattering of visible light, producing a cloudy appearance. This optical phenomenon, called the Tyndall effect, distinguishes colloidal dispersions from perfectly transparent molecular solutions.
33. The cleaning action of detergents is most effective in:
[RRB Group D (2025 recruitment cycle), Shift 2 — 11 Aug 2026]
(A) Neutral medium
(B) Acidic medium
(C) Alkaline medium
(D) Highly acidic medium
Answer: (C) Alkaline medium
Explanation: Many laundry detergents are formulated for mildly alkaline conditions. Alkalinity helps loosen fatty soils, improves certain cleaning additives, and reduces the redeposition of dirt. The precise optimal pH depends on the detergent formulation and fabric; this question refers to conventional alkaline laundry formulations.
32. Why is soap less effective in hard water?
[RRB Group D (2025 recruitment cycle), Shift 1 — 9 Aug 2026]
(A) Soap evaporates quickly
(B) Soap forms insoluble scum
(C) Soap becomes acidic
(D) Soap loses its polarity
Answer: (B) Soap forms insoluble scum
Explanation: Hard water contains calcium and magnesium ions, which react with fatty-acid carboxylate ions in soap. The resulting insoluble calcium or magnesium salts form scum. This reaction consumes soap before it can form cleaning micelles, reducing lather and washing efficiency.
31. How does saponification relate to soap formation?
[RRB Group D (2025 recruitment cycle), Shift 1 — 6 Aug 2026]
(A) Saponification produces only esters used in flavoring
(B) Saponification makes ethanol for cleaning
(C) Saponification is unrelated to soap production
(D) Saponification produces sodium or potassium salts of long-chain carboxylic acids, which are soaps
Answer: (D) Saponification produces sodium or potassium salts of long-chain carboxylic acids, which are soaps
Explanation: Saponification is the alkaline hydrolysis of triglycerides found in fats and oils. Sodium hydroxide or potassium hydroxide breaks ester bonds, producing glycerol and the corresponding fatty-acid salts. These salts are soaps, with long oil-attracting chains and water-attracting ionic groups.
30. In the saponification process, triglycerides are reacted with which alkali to produce glycerol and fatty acid salts called “soaps”?
[DSSSB Assistant Superintendent, Paper I & II, Shift 2 — 5 Jul 2026]
(A) NaOH
(B) Mg(OH)₂
(C) Ca(OH)₂
(D) Ba(OH)₂
Answer: (A) NaOH
Explanation: Sodium hydroxide is the usual alkali for manufacturing solid soap. It cleaves the three ester linkages of a triglyceride, yielding glycerol and sodium salts of fatty acids. Potassium hydroxide can instead produce softer soaps, but it is not among these options.
29. The cleansing action of soap is due to which of its properties?
[RRB Group D, Shift 1 — 23 Dec 2025]
(A) Being a strong acid
(B) Being a strong base
(C) High melting point
(D) Ability to form micelles
Answer: (D) Ability to form micelles
Explanation: Soap molecules aggregate into micelles with non-polar hydrocarbon interiors and water-loving outer surfaces. Grease becomes enclosed within these structures and is carried into the washing water. Micelle formation and emulsification, rather than high acidity or melting point, explain soap’s cleansing action.
28. Soap molecules arrange themselves in which form to perform cleaning action?
[RRB Group D, Shift 2 — 21 Dec 2025]
(A) Micelles
(B) Precipitation
(C) Crystal
(D) Colloid
Answer: (A) Micelles
Explanation: The spherical assemblies formed by soap molecules are called micelles. Their non-polar tails gather inside, where they can hold oily dirt, while charged heads remain exposed to water. Agitation then carries the suspended grease-containing particles away during rinsing.
27. What is the hydrophilic end of a soap molecule like?
[RRB Group D, Shift 3 — 15 Dec 2025]
(A) Ionic and reacts with water
(B) Neutral and non-polar
(C) Non-ionic and soluble in water
(D) Non-ionic and soluble in oil
Answer: (A) Ionic and reacts with water
Explanation: The hydrophilic portion of an ordinary soap molecule is its charged carboxylate head, represented as –COO⁻. It interacts favorably with polar water molecules. The opposite end is a long hydrocarbon tail that associates with oils and other non-polar substances.
26. Detergents can work in which of the following?
[RRB Group D, Shift 3 — 5 Dec 2025]
(A) Only distilled water
(B) Only hot water
(C) Only soft water
(D) Both hard and soft water
Answer: (D) Both hard and soft water
Explanation: Most synthetic detergents retain cleaning effectiveness in both soft and hard water. Their common sulphate or sulphonate surfactants generally do not produce the same insoluble scum as fatty-acid soaps in the presence of calcium and magnesium ions.
25. Which statement is most accurate regarding soap?
[DSSSB PGT Chemistry, Shift 1 — 22 Jul 2025]
(A) Soap micelles have hydrophobic interiors and hydrophilic surfaces
(B) Soap molecules do not contain ionic heads and non-polar tails
(C) Soap is chemically identical to synthetic detergents
(D) Soap works equally well in hard and soft water
Answer: (A) Soap micelles have hydrophobic interiors and hydrophilic surfaces
Explanation: In water, non-polar soap tails orient towards the centre of a micelle, making its interior hydrophobic. The negatively charged head groups remain outside, in contact with water. This organization stabilizes dispersed oily material and permits its removal during washing.
24. Which of the following has two ends: one which is hydrophilic and the other which is hydrophobic?
[RRB Technician Grade III, Shift 3 — 28 Dec 2024]
(A) Water
(B) Perfume
(C) Cream
(D) Soap
Answer: (D) Soap
Explanation: Soap is amphiphilic: its charged carboxylate head is attracted to water, while its long hydrocarbon tail avoids water and associates with grease. This two-part molecular architecture lets soap bridge oil and water, aiding emulsification and removal of dirt.
23. Which of the following is a common drawback of using soap in hard water?
[RRB Technician Grade III, Shift 2 — 24 Dec 2024]
(A) Soap dissolves too quickly in hard water
(B) Formation of soap scum due to the reaction with calcium and magnesium ions
(C) Soap creates too much lather
(D) Soap loses its colour in hard water
Answer: (B) Formation of soap scum due to the reaction with calcium and magnesium ions
Explanation: Hard-water calcium and magnesium ions combine with soap anions to form water-insoluble fatty-acid salts. These collect as soap scum, consume the cleaning agent, and prevent efficient lather formation. Synthetic detergents usually perform better because their surfactants resist such precipitation.
22. What is the chemical reaction that occurs when fats or oils combine with a strong alkali, such as sodium hydroxide, to make soap?
[SSC JE Civil, Shift 1, Paper 1 — 7 Jun 2024]
(A) Saponification
(B) Combustion
(C) Fermentation
(D) Oxidation
Answer: (A) Saponification
Explanation: When triglyceride fats or oils react with aqueous sodium hydroxide, their ester bonds undergo alkaline hydrolysis. Glycerol and sodium fatty-acid salts are produced. This characteristic soap-making reaction is called saponification, not combustion, fermentation, or oxidation.
21. Consider the following pairs:
1. Quick lime: Manufacture of cement;
2. Slaked lime: Preparation of soap;
3. Plaster of Paris: Making toys.
How many of the above pairs are correctly matched?
[HPSC Preliminary Examination, General Studies — 11 Feb 2024]
(A) Only one pair
(B) Only two pairs
(C) All three pairs
(D) None of the pairs
(E) Question not attempted
Answer: (B) Only two pairs
Explanation: Quicklime is used in cement manufacture, and plaster of Paris is employed in moulds and toys. Ordinary soap production mainly involves fats and sodium or potassium hydroxide, not slaked lime. Thus, the first and third pairs are correct.
20. What are soaps?
[EMRS Lab Attendant — 23 Dec 2023]
(A) Salts of silicates
(B) Mixtures of glycerol and alcohols
(C) Sodium or potassium salts of heavier fatty acids
(D) Esters of heavy fatty acids
Answer: (C) Sodium or potassium salts of heavier fatty acids
Explanation: Chemically, common soaps are sodium or potassium salts of higher fatty acids, such as stearic and palmitic acids. They arise through saponification of fats and oils. Glycerol is a by-product of preparation, while the starting fats themselves are esters.
19. What is used to make transparent soaps?
[Delhi Police Constable (Executive), Shift 3 — 23 Nov 2023]
(A) Sodium chloride
(B) Ethanol
(C) Rosin
(D) Sodium carbonate
Answer: (B) Ethanol
Explanation: Ethanol can dissolve and homogenize the soap mixture during the manufacture of transparent bars. Proper solvent processing reduces light-scattering irregularities and improves clarity. Sodium chloride is more commonly used for salting soap out, rather than making it transparent.
18. Soap forms a precipitate in ____ water.
[MP Police Constable, Shift 1 — 20 Aug 2023]
(A) Cold
(B) Foam
(C) Soft
(D) Hard
Answer: (D) Hard
Explanation: Hard water contains soluble salts of calcium and magnesium. Their ions combine with the fatty-acid anions of soap to form insoluble salts, seen as a precipitate or scum. As a result, less soap remains available for cleansing and lathering.
17. Which one of the following is not a soap?
[UPSC EPFO APFC — 2 Jul 2023]
(A) Sodium stearate
(B) Sodium palmate
(C) Sodium benzoate
(D) Sodium oleate
Answer: (C) Sodium benzoate
Explanation: Sodium stearate, palmate, and oleate are salts of long-chain fatty acids and can function as soaps. Sodium benzoate is derived from aromatic benzoic acid rather than a long-chain fatty acid. It is mainly used as a preservative, not a traditional soap.
16. Which among the following substances is used in moisturizing creams and soaps because of its hygroscopic properties?
[SSC MTS (2022 cycle), Shift 2 — 2 May 2023]
(A) Galena
(B) Ethanol
(C) Freon
(D) Glycerol
Answer: (D) Glycerol
Explanation: Glycerol, also called glycerin, is a humectant: it attracts and retains water. In soaps and moisturizers it helps limit drying and improves skin feel. Glycerol is also generated when triglycerides are hydrolysed during conventional soap manufacture.
15. Which of the following is not used in the preparation of soap?
[Rajasthan CET Senior Secondary, Shift 1 — 5 Feb 2023]
(A) Stearic acid
(B) Lauric acid
(C) Benzoic acid
(D) Palmitic acid
Answer: (C) Benzoic acid
Explanation: Stearic, lauric, and palmitic acids are long-chain fatty acids whose sodium or potassium salts are soaps. Benzoic acid contains an aromatic ring instead of a long hydrocarbon tail, so its salt is not an ordinary cleansing soap.
14. Which of the following statements is TRUE with respect to soaps?
[Delhi Police Head Constable (AWO/TPO), Shift 2 — 28 Oct 2022]
(A) Soaps that float in water are made by dissolving the soap in ethanol and then evaporating the excess solvent
(B) Transparent soaps are made by beating tiny air bubbles before their hardening
(C) Shaving soaps contain glycerol to prevent rapid drying
(D) Toilet soaps contain fillers like sodium rosinate, sodium silicate, borax and sodium carbonate
Answer: (C) Shaving soaps contain glycerol to prevent rapid drying
Explanation: Glycerol is added to shaving soap as a moisture-retaining agent, helping the soap and lather remain usable instead of drying rapidly. Floating soaps are made by entraining air; ethanol helps transparency. Industrial fillers are more characteristic of laundry soaps.
13. Which of the following statements are CORRECT about soap?
(I) Transparent soaps are made by dissolving soap in ethanol and evaporating excess solvent.
(II) Shaving soaps contain sodium rosinate to prevent rapid drying.
(III) Dye does not absorb evenly on cloth washed with soap using hard water because of an insoluble gummy precipitate.
[Delhi Police Head Constable (AWO/TPO), Shift 1 — 27 Oct 2022]
(A) I and II
(B) I and III
(C) II and III
(D) I, II and III
Answer: (B) I and III
Explanation: Ethanol can be used in producing transparent soap, and hard-water ions create gummy soap scum that interferes with fabric treatment. Statement II misidentifies sodium rosinate as the anti-drying additive; glycerol is primarily added to retain moisture in shaving soap.
12. Which of the following is left in the sodium hydroxide solution after removing the soap?
[Delhi Police Head Constable (AWO/TPO), Shift 3 — 27 Oct 2022]
(A) Alcohol
(B) Glycerol
(C) Esters
(D) Phenol
Answer: (B) Glycerol
Explanation: During saponification, a triglyceride reacts with sodium hydroxide to yield soap and glycerol. When the relatively insoluble soap is separated, glycerol remains dissolved in the aqueous layer. It is a valuable three-hydroxyl alcohol used in cosmetics and pharmaceuticals.
11. Which inorganic compound is used to manufacture soap, rayon, paper, explosives, dyes, and petroleum products?
[SSC CHSL (2021 cycle), Shift 1 — 25 May 2022]
(A) NaOCl
(B) NaOH
(C) CaOCl₂
(D) NaHCO₃
Answer: (B) NaOH
Explanation: Sodium hydroxide is caustic soda, a strong alkali used to saponify fats in soap manufacturing. It also serves in paper pulping, textile processing, and various chemical industries. Sodium hypochlorite and bleaching powder instead are mainly valued as oxidizing or bleaching agents.
10. The hardness of water is estimated by
[WBCS Mains 2021, Paper IV (held May 2022) — May 2022]
(A) Conductivity method
(B) EDTA method
(C) Titrimetric method
(D) Distillation method
Answer: (B) EDTA method
Explanation: EDTA complexometric titration measures calcium and magnesium ions responsible for water hardness. These ions otherwise react with soap to produce scum. The method uses a suitable indicator, often Eriochrome Black T, to identify the titration endpoint and calculate total hardness.
9. Detergents are –
[UPPSC GIC Lecturer, Chemistry — 2021]
(A) Triglycerides of fatty acids
(B) Sodium salts of higher fatty acids
(C) Sodium salts of alkyl sulphonates
(D) Hydrogenated products of long-chain fatty acids
Answer: (C) Sodium salts of alkyl sulphonates
Explanation: Common synthetic anionic detergents include sodium alkyl sulphonates and related sulphates. They have long hydrocarbon chains and polar cleaning groups. In contrast, sodium salts of higher fatty acids are conventional soaps, which can form scum with hard-water minerals.
8. Which of the following can be used as soap?
[Bihar STET PGT Chemistry, Paper II, Shift 1 — 18 Sept 2020]
(A) C₁₇H₃₅COONa
(B) (C₁₇H₃₅COO)₂Ca
(C) C₁₇H₃₅COOH
(D) C₁₇H₃₁COOH
Answer: (A) C₁₇H₃₅COONa
Explanation: C₁₇H₃₅COONa is sodium stearate, a sodium salt of the long-chain fatty acid stearic acid. It functions as soap. Calcium stearate is poorly water-soluble, while the free carboxylic acids listed are not themselves sodium or potassium soaps.
7. What is the dominant chemical present in detergent powder?
[SSC CGL, Shift 1 — 12 Jun 2019]
(A) Calcium carbonate
(B) Sodium carbonate
(C) Hydrochloric acid
(D) Sodium alkyl sulphate
Answer: (B) Sodium carbonate
Explanation: Sodium carbonate, known as soda ash or washing soda in hydrated form, is a common major builder in many powdered laundry detergents. It provides alkalinity and helps soften water. The actual dominant ingredient varies by brand and formulation; the recorded exam key identifies sodium carbonate.
6. Which of the following is a non-biodegradable detergent?
[MP HSTET Varg 1 (2018 cycle), Chemistry, Shift 1 — 7 Feb 2019]
(A) Sodium-4-(1-dodecyl)benzenesulphonate
(B) Sodium-4-(1,3,5,7-tetramethyloctyl)benzenesulphonate
(C) Sodium-4-(2-dodecyl)benzenesulphonate
(D) Sodium lauryl sulphate
Answer: (B) Sodium-4-(1,3,5,7-tetramethyloctyl)benzenesulphonate
Explanation: The second compound contains a highly branched hydrocarbon chain, making it difficult for many microorganisms to degrade. Linear detergent chains are generally broken down more readily. Persistent branched surfactants can contribute to foaming and pollution in receiving water bodies.
5. Which of the following statements are CORRECT?
I. Soap molecules form structures called micelles.
II. Soap micelles cannot scatter light.
III. Oily dirt gets collected in the centre of the micelle.
[SSC CHSL, Shift 1 — 22 Mar 2018]
(A) Both I and II
(B) Both I and III
(C) Both II and III
(D) All I, II and III
Answer: (B) Both I and III
Explanation: Soap molecules aggregate into micelles in water, and grease becomes trapped within their non-polar cores. Statement II is incorrect because micelles are colloidal particles capable of scattering light. Therefore statements I and III, but not II, are correct.
4. If one mixes up ashes with animal fat, the substance received in the crude form is called?
[UPSC NDA, General Ability Test — 18 Sept 2016]
(A) Pheromone
(B) Soap
(C) Cement
(D) Concrete
Answer: (B) Soap
Explanation: Wood ash traditionally supplied alkaline substances, which react with animal fats to form crude soap through saponification. The resulting fatty-acid salts can emulsify greasy matter. This early method preceded modern production with precisely measured sodium or potassium hydroxide solutions.
3. Cleansing action of soap occurs because
[Punjab Civil Service, Paper I — 2015]
(A) Oil and grease can be absorbed into the hydrophobic centres of soap micelles and get washed away
(B) Oil and grease can be absorbed into the hydrophilic centres of soap micelles and washed away
(C) Oil and grease can be absorbed into both hydrophilic and hydrophobic centres but not washed away
(D) Cleansing action is not related to micelles
Answer: (A) Oil and grease can be absorbed into the hydrophobic centres of soap micelles and get washed away
Explanation: Oily material is non-polar and associates with the hydrophobic interior of soap micelles. Hydrophilic carboxylate groups on the outer surface interact with water and stabilize the dispersion. This arrangement allows greasy dirt to be lifted and rinsed away.
2. The cleaning action of soap and detergent in water is due to the formation of
[UPSC NDA, General Ability Test — 19 Apr 2015]
(A) Micelle
(B) Salt
(C) Base
(D) Acid
Answer: (A) Micelle
Explanation: Surfactant molecules form micelles that surround non-polar dirt while exposing water-loving groups outward. This creates dispersed grease droplets that can be removed with water. Formation of an acid, base, or ordinary salt alone does not explain the cleaning mechanism.
1. Soaps are
[WBPSC Miscellaneous Preliminary Examination (2012 cycle), Shift 2 — 19 May 2013]
(A) Sodium and potassium salts of higher fatty acids
(B) Sodium salts of sulphonic acids
(C) High molecular mass alcohols
(D) Mixtures of glycerol and phenol
Answer: (A) Sodium and potassium salts of higher fatty acids
Explanation: Soaps are sodium or potassium salts of long-chain fatty acids, usually obtained when vegetable oils or animal fats undergo alkaline hydrolysis. Sodium salts of sulphonic acids more commonly describe certain synthetic detergents, while glycerol is a by-product of soap manufacture.