Common Organic Compounds in Daily Life – NDA Chemistry PYQs

Solve NDA Chemistry previous-year questions on Common Organic Compounds with detailed solutions and explanations.

Chapter-wise PYQs • Concept-based explanations • Exam insights

NDA 2026-II

Q. 1. Coconut oil upon hydrolysis with potassium hydroxide gives :

(a) Free fatty acids and sodium hydroxide

(b) Glycerol and sodium salts of fatty acids

(d) Glycerol and potassium salts of fatty acids

Answer: (d) Glycerol and potassium salts of fatty acids

Explanation: Saponification: fat/oil + KOH → glycerol + potassium salts of fatty acids (soft soap). Coconut oil is a triglyceride (ester of glycerol with fatty acids). Hydrolysis with KOH gives glycerol and K-salts of the fatty acids (soft soap). Concept Tested: Saponification of coconut oil with KOH – glycerol + potassium soaps

NDA 2025-I

Q. 2. Which one of the following statements is NOT correct?

(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

(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

Explanation: In micelles, it is the opposite: the hydrophobic (non-ionic) tail points INWARD towards the oil droplet, and the ionic (hydrophilic) head points OUTWARD towards water. So (d) is NOT correct. Concept Tested: Micelle structure- hydrophobic tail inside, ionic head outside

NDA 2023-II

Q. 3. What is the action of litmus on ethanol ?

(a) Litmus is neutral towards ethanol

(b) Ethanol turns blue litmus to red; confirming acidic nature of ethanol

(d) Ethanol decolorizes litmus through bleaching action

Answer: (a) Litmus is neutral towards ethanol

Explanation: Ethanol (C₂H₅OH) is a neutral molecule- it does not ionise in water to produce H⁺ or OH⁻ ions. Therefore it does not change litmus colour. Concept Tested: Ethanol is neutral – no effect on litmus

NDA 2023-I

Q. 4. What is the specific purpose of using potassium hydroxide during the saponification process ?

(a) To obtain soaps which are hard on the skin

(b) To obtain soaps which are soft on the skin

(d) To make the saponification very economical

Answer: (b) To obtain soaps which are soft on the skin

Explanation: KOH produces soft soaps (potassium soaps), which are more soluble and gentle. NaOH produces hard soaps. Soft soaps are preferred for liquid soaps and shaving creams. Concept Tested: KOH in saponification – produces soft soap

NDA 2021-I

Q. 5. Which one of the following statements about the cleansing action of soap is not true?

(a) The oil and dirt gets collected in the centre of the micelle.

(b) Soap micelles scatter light.

(d) Soap forms insoluble precipitates with the calcium and magnesium ions in hard water.

Answer: (c) Soaps are ammonium salts of long chain carboxylic acids.

Explanation: Soaps are sodium or potassium salts of long-chain carboxylic acids, NOT ammonium salts. Options (a), (b) and (d) are all correct – dirt collects in micelle centre, micelles scatter light (Tyndall effect), and soaps form insoluble precipitates with hard water minerals. Concept Tested: Soap composition – Na/K salts, not ammonium salts

NDA 2020

Q. 6. Vinegar is also known as

(a) ethanoic acid

(b) nitric acid

(d) tartaric acid

Answer: (a) ethanoic acid

Explanation: Vinegar = dilute ethanoic acid (acetic acid, CH₃COOH). Ethanoic is the IUPAC name for acetic acid. Concept Tested: Vinegar = ethanoic acid (IUPAC name for acetic acid)

NDA 2019-II

Q. 7. A sample of ‘soft soap’ contains

(a) Caesium

(b) Potassium

(d) Magnesium

Answer: (b) Potassium

Explanation: Soft soap is made by saponification with potassium hydroxide (KOH), forming potassium salts of fatty acids. Hard soap is made with NaOH (sodium). Potassium soaps are softer and more soluble. Concept Tested: Soft soap = potassium salt of fatty acid

Q. 8. Soaps clean surfaces on the principle based on

(a) Viscosity

(b) Floatation

(d) Surface tension

Answer: (d) Surface tension

Explanation: Soap cleans by reducing surface tension, allowing water to spread and penetrate better. The soap molecules form micelles around dirt particles, emulsifying them. Concept Tested: Soap cleaning – based on surface tension reduction

NDA 2019-I

Q. 9. Which one of the following is NOT a synthetic detergent?

(a) CH₃(CH₂)₁₀CH₂O SO₃⁻ Na⁺

(b) [CH₃(CH₂)₁₅–N–(CH₃)₃]⁺ Br⁻

(d) CH₃(CH₂)₁₆COO(CH₂CH₂O)ₙ CH₂CH₂OH

Answer: (c) CH₃(CH₂)₁₆COO⁻ Na⁺

Explanation: CH₃(CH₂)₁₆COO⁻ Na⁺ is sodium stearate – the sodium salt of a fatty acid. This is a natural soap, not a synthetic detergent. Options (a), (b) and (d) are synthetic detergents: (a) is an anionic SLS-type detergent; (b) is a cationic detergent; (d) is a non-ionic detergent. Concept Tested: Distinguishing natural soap from synthetic detergent

NDA 2016-II

Q. 10. If one mixes up ashes with animal fat, the substance received in the crude form is called

(a) Pheromone

(b) Soap

(d) Concrete

Answer: (b) Soap

Explanation: The crude earliest form of soap was made by mixing wood ash (which contains potassium carbonate/hydroxide) with animal fat. This is the original saponification process. This is how soap was made in ancient times. Concept Tested: Ancient soap making – ash (alkali) + animal fat

NDA 2016-I

Q. 11. Soap is sodium or potassium salt of

(a) Stearic acid

(b) Oleic acid

(d) All of the above

Answer: (d) All of the above

Explanation: Soap can be the sodium or potassium salt of stearic acid (C₁₇H₃₅COOH), oleic acid (C₁₇H₃₃COOH), or palmitic acid (C₁₅H₃₁COOH) – all are long-chain fatty acids. Most soap is a mixture of these salts. Concept Tested: Soap – Na/K salt of stearic, oleic, or palmitic acid

NDA 2015-II

Q. 12. The main constituent of Vinegar is:

(a) Acetic acid

(b) Ascorbic acid

(d) Tartaric acid

Answer: (a) Acetic acid

Explanation: Same repeated question on vinegar. The main constituent is acetic acid (ethanoic acid, CH₃COOH). Concept Tested: Vinegar = acetic acid (repeated)

NDA 2015-I

Q. 13. The cleaning action of soap and detergent in water is due to the formation of

(a) Micelle

(b) Salt

(d) Acid

Answer: (a) Micelle

Explanation: When soap or detergent is added to water, the molecules arrange themselves into spherical structures called micelles. The hydrophobic tails point inward (towards grease) and the hydrophilic heads point outward (towards water). This allows soap to emulsify fats and remove dirt. Concept Tested: Micelle formation – cleaning action of soap

★ JOVIK Exam Insight: Micelle = key to soap cleaning. The hydrophobic tail traps oil; the hydrophilic head faces water.

NDA 2014-II

Q. 14. Which one of the following substances is most likely to be used as soap?

(a) CH₃(CH₂)₁₂COOCH₃

(b) CH₃(CH₂)₅O(CH₂)₅CH₃

(d) CH₃(CH₂)₁₂CHCl₂

Answer: (c) CH₃(CH₂)₁₂COONa

Explanation: Soap is the sodium salt of a long-chain fatty acid. CH₃(CH₂)₁₂COONa is sodium myristate – a sodium salt of a long-chain carboxylic acid. (a) is a methyl ester, (b) is an ether, (d) contains a dichloro group. Concept Tested: Identifying a soap molecule – sodium salt of fatty acid

NDA 2013-I

Q. 15. The principle of cleaning by soap is

(a) surface tension

(b) floatation

(d) elasticity

Answer: (a) surface tension

Explanation: Soap cleans by reducing the surface tension of water, allowing it to wet surfaces better. The hydrophobic tails of soap molecules surround oily/greasy dirt, and the hydrophilic heads attract water, forming micelles that carry dirt away. Concept Tested: Cleaning action of soap – reduces surface tension, forms micelles

Q. 16. Sodium stearate is a salt and is used

(a) in gunpowder

(b) in paint

(d) to make fertilizer

Answer: (c) to make soap

Explanation: Sodium stearate (C₁₇H₃₅COONa) is the sodium salt of stearic acid and is the main component of hard soap. It is made by saponification of fats with NaOH. Concept Tested: Sodium stearate – main ingredient of hard soap

Q. 17. The acid contained in vinegar is

(a) acetic acid

(b) ascorbic acid

(d) tartaric acid

Answer: (a) acetic acid

Explanation: Vinegar contains acetic acid (ethanoic acid, CH₃COOH). This is one of the most frequently repeated facts in NDA chemistry. Concept Tested: Vinegar = acetic acid (repeated)

NDA 2011-II

Q. 18. The main constituent of vinegar is

(a) Citric acid

(b) Acetic acid

(d) Tartaric acid

Answer: (b) Acetic acid

Explanation: Acetic acid (ethanoic acid, CH₃COOH) is the main constituent of vinegar (4–8% solution). Concept Tested: Main constituent of vinegar – acetic acid

Q. 19. The reaction that takes place in soap making is called saponification. Basically soap is sodium or potassium salts of

(a) long chain monocarboxylic acids

(b) glycerol

(d) long chain tricarboxylic acids

Answer: (a) long chain monocarboxylic acids

Explanation: Soap is the sodium (or potassium) salt of long-chain monocarboxylic (fatty) acids such as stearic acid (C₁₇H₃₅COOH), palmitic acid (C₁₅H₃₁COOH) and oleic acid. Saponification = hydrolysis of fats/oils with NaOH or KOH. Concept Tested: Saponification – soap is Na/K salt of long-chain monocarboxylic acids

NDA 2010-I

Q. 20. Vinegar is produced from

(a) ethanoic acid

(b) valeric acid

(d) butanoic acid

Answer: (a) ethanoic acid

Explanation: Vinegar is dilute ethanoic acid (acetic acid, CH₃COOH). It is produced by the fermentation of ethanol by acetic acid bacteria. Concept Tested: Vinegar = ethanoic acid (acetic acid)

NDA 2009-II

Q. 21. 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?

(a) 1 and 2

(b) 2 and 3

(d) 1 only

Answer: (a) 1 and 2

Explanation: Statement 1: Correct – soap forms insoluble fatty acids in acidic water (Ca²⁺, Mg²⁺ ions also cause soap scum). Statement 2: Correct – soap’s ionic part is —COO⁻Na⁺ (sodium carboxylate). Statement 3: Incorrect – soap does not necessarily dissolve faster than detergent; detergents are often more soluble in cold water. Concept Tested: Properties of soap – acidic water problem and ionic structure

Q. 22. Assertion (A): On a wet floor of a bathroom, a small circular area around a pinch of foam appears to be dry. Reason (R): Soap molecules reduce surface tension and increase surface area of the thin layer of water on the wet floor.

(a) Both A and R are individually true and R is the correct explanation of A

(b) Both A and R are individually true but R is not the correct explanation of A

(d) A is false but R is true

Answer: (a) Both A and R are individually true and R is the correct explanation of A

Explanation: Soap reduces surface tension. When foam (soap) is on a wet floor, it spreads the thin water film outward, making the area directly under the foam appear dry. The Reason correctly explains the Assertion. Concept Tested: Soap reducing surface tension – spreading of water film