Industrial Chemistry – NDA Chemistry PYQs

Solve NDA Chemistry previous-year questions on Industrial Chemistry with detailed solutions and explanations.

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

NDA 2026-II

Q. 1. Which of the following statements is/are correct in respect of Portland cement ?

I. Adding more water (higher water-cement ratio) accelerates the initial setting time of cement.

II. The addition of a small percentage of gypsum gives the desired retardation.

III. Gypsum is added during manufacturing to accelerate the setting time of cement.

Select the answer using the code given below :

(a) I and II

(b) I and III

(d) II only

Answer: (d) II only

Explanation: Statement I: Incorrect – more water (higher water-cement ratio) generally weakens cement and may slow initial set, not accelerate it. Statement II: Correct – gypsum retards (slows) the setting of cement, providing the desired control. Statement III: Incorrect – gypsum RETARDS (slows) setting time, not accelerates it. Only Statement II is correct. Concept Tested: Gypsum in cement – retarder, slows setting time

NDA 2026-I

Q. 2. Which of the following is/are the physical test(s) employed for the manufacture of paper?

I. Mechanical and strength properties

II. Surface properties

III. Optical properties

IV. Permeability to fluids

Select the correct answer using the code given below.

(a) I only

(b) II and III only

(d) I, II, III and IV

Answer: (d) I, II, III and IV

Explanation: In paper manufacturing, quality testing includes mechanical and strength properties (tensile strength, tear, burst), surface properties (smoothness, porosity), optical properties (brightness, opacity, colour), and permeability to fluids (water absorption). All four are standard physical tests for paper quality. Concept Tested: Physical tests for paper manufacture – all four categories

NDA 2025-II

Q. 3. Which one of the following is NOT present in cement?

(a) 2CaO·SiO₂

(b) 3CaO·SiO₂

(d) 3CaO·Al₂O₃

Answer: (c) 4CaO·SiO₂

Explanation: Portland cement contains: 3CaO·SiO₂ (C₃S, alite ~50–70%), 2CaO·SiO₂ (C₂S, belite ~15–30%), 3CaO·Al₂O₃ (C₃A, ~5–10%), and 4CaO·Al₂O₃·Fe₂O₃ (C₄AF). The compound 4CaO·SiO₂ (tetracalcium silicate) is NOT a standard component of Portland cement. Concept Tested: Portland cement compounds – 4CaO·SiO₂ is not present

NDA 2024-I

Q. 4. Which among the following are essential constituents of Portland cement?

(a) Sand, lime, clay

(b) Silica, alumina, lime

(d) Sand, graphene, clay

Answer: (b) Silica, alumina, lime

Explanation: Essential constituents of Portland cement: SiO₂ (silica), Al₂O₃ (alumina), and CaO (lime). These react during clinkerisation to form the calcium silicates and aluminates that give cement its strength. Concept Tested: Essential constituents of Portland cement – silica, alumina, lime

NDA 2023-I

Q. 5. For manufacturing of glass, which among the following is used as a source of silica ?

(a) Fine clay soil

(b) Wood powder

(d) Sand

Answer: (d) Sand

Explanation: Sand (SiO₂) is the primary source of silica for glass manufacturing. Pure quartz sand is used in high-quality glass. Fine clay contains SiO₂ but also impurities. Concept Tested: Source of silica for glass – sand

NDA 2021-I

Q. 6. Which one of the following is not used as a raw material in the manufacture of glass?

(a) Soda

(b) Alumina

(d) Gypsum

Answer: (d) Gypsum

Explanation: Glass is made from silica (SiO₂), soda (Na₂CO₃), and lime (CaCO₃) for ordinary soda-lime glass, or borax (B₂O₃) for borosilicate glass. Alumina (Al₂O₃) can also be added. Gypsum (CaSO₄·2H₂O) is not used in glass making – it is used in cement. Concept Tested: Glass manufacture – gypsum is not a raw material

NDA 2019-II

Q. 7. Which one of the following statements about glass is not correct?

(a) Glass is often said to be a supercooled liquid.

(b) Glass has no definite melting point.

(d) Boron is present in pyrex glass.

Answer: (c) Soda glass is harder than pyrex glass.

Explanation: Pyrex is borosilicate glass – it is harder, more heat-resistant and chemically more durable than ordinary soda glass. So (c) is NOT correct – soda glass is softer than pyrex. Options (a), (b) and (d) are all correct. Concept Tested: Comparison of soda glass and pyrex glass – pyrex is harder

Q. 8. The raw materials used for the manufacture of Portland cement are

(a) Lime, silica and sulphur dioxide

(b) Lime, silica and carbon dioxide

(d) Lime, silica and boric acid

Answer: (c) Lime, silica and alumina

Explanation: Portland cement raw materials: lime (CaO from limestone), silica (SiO₂ from clay), and alumina (Al₂O₃ from clay). Together they form calcium silicates and aluminates. SO₂, CO₂, and boric acid are not raw materials. Concept Tested: Portland cement raw materials – lime, silica, alumina

NDA 2017-I

Q. 9. Glass is a

(a) liquid

(b) colloid

(d) crystalline solid

Answer: (c) non-crystalline amorphous solid

Explanation: Glass is an amorphous solid – it does not have an ordered crystalline structure. At room temperature it behaves as a solid. It is also described as a supercooled liquid, but among these options, non-crystalline amorphous solid is the most precise description. Concept Tested: Nature of glass – amorphous solid

NDA 2016-II

Q. 10. The setting time of cement is lowered by adding

(a) oxides of aluminium

(b) gypsum

(d) silica

Answer: (a) oxides of aluminium

Explanation: Aluminium oxide (Al₂O₃) / alumina increases the proportion of C₃A in cement, which accelerates setting. Gypsum retards (increases) setting time. Oxides of magnesium and silica do not specifically lower the setting time. Note: this question is notable because gypsum is typically known as a retarder – option (b) is a common trap. Concept Tested: Lowering cement setting time – aluminium oxide (not gypsum)

NDA 2015-II

Q. 11. Addition of gypsum to cement:

(a) reduces setting time of cement

(b) produces very light colour cement

(d) shining surface is formed

Answer: (c) increases setting time of cement

Explanation: Gypsum (CaSO₄·2H₂O) is added to cement clinker to slow down (retard) the setting process. Without gypsum, cement sets too quickly – called “flash set.” Gypsum reacts with C₃A (tricalcium aluminate) in cement to form ettringite, which slows the setting. Concept Tested: Role of gypsum in cement – retarder, increases setting time

★ JOVIK Exam Insight: Gypsum added to cement INCREASES (retards) setting time. NDA tests this distinction – confusing whether gypsum increases or decreases setting time.

NDA 2014-II

Q. 12. Optical glass used in the construction of spectacles is made by

(a) flint glass

(b) Crookes glass

(d) hard glass

Answer: (a) flint glass

Explanation: Flint glass (containing lead oxide, PbO) has a high refractive index and is used for optical lenses in spectacles, cameras and microscopes. Crookes glass absorbs UV radiation. Concept Tested: Optical glass for spectacles – flint glass

NDA 2013-II

Q. 13. Statement I: Glass is not considered as a true compound. Statement II: Glass does not have a definite melting point.

(a) Both the statements are individually true and Statement II is the correct explanation of Statement I

(b) Both the statements are individually true but Statement II is not the correct explanation of Statement I

(d) Statement I is false but Statement II is true

Answer: (b) Both the statements are individually true but Statement II is not the correct explanation of Statement I

Explanation: Glass is not a true compound because it has no fixed chemical formula – it is a mixture of silicates (Statement I correct). Glass has no definite melting point, softening over a range of temperatures because it is amorphous (Statement II correct). However, Statement II (no definite melting point) does not explain why glass is not a compound. Both are true but II does not explain I. Concept Tested: Glass – not a compound; no definite melting point

NDA 2012-II

Q. 14. The most important raw materials used in the manufacture of cement are

(a) Potassium nitrate, charcoal and sulphur

(b) Limestone, clay and gypsum

(d) Limestone, sodium carbonate and silica

Answer: (b) Limestone, clay and gypsum

Explanation: Cement is made from limestone (CaCO₃) as the main calcium source, clay (providing SiO₂ and Al₂O₃), and gypsum (CaSO₄·2H₂O, added to control setting time). Option (a) describes gunpowder. Concept Tested: Raw materials for cement manufacture – limestone, clay, gypsum

NDA 2012-I

Q. 15. Which one among the following is the correct order of amount of lime (CaO), silica (SiO₂), alumina (Al₂O₃) and ferric oxide (Fe₂O₃) in Portland cement?

(a) CaO > SiO₂ > Al₂O₃ > Fe₂O₃

(b) SiO₂ > CaO > Fe₂O₃ > Al₂O₃

(d) Fe₂O₃ > Al₂O₃ > SiO₂ > CaO

Answer: (a) CaO > SiO₂ > Al₂O₃ > Fe₂O₃

Explanation: Portland cement composition (approximate): CaO 60–67%, SiO₂ 17–25%, Al₂O₃ 3–8%, Fe₂O₃ 0.5–6%. The correct decreasing order is CaO > SiO₂ > Al₂O₃ > Fe₂O₃. Concept Tested: Portland cement composition – CaO > SiO₂ > Al₂O₃ > Fe₂O₃

NDA 2011-II

Q. 16. The major component used in preparation of different types of glasses is

(a) Silica

(b) Sodium borate

(d) Sodium silicate

Answer: (a) Silica

Explanation: Silica (SiO₂) is the major component of all types of glass. Soda-lime glass = SiO₂ + Na₂O + CaO. Pyrex glass = SiO₂ + B₂O₃ (borosilicate glass). Silica is the essential glass-forming oxide. Concept Tested: Major component of glass – silica (SiO₂)

Q. 17. Match List I with List II and select the correct answer using the code given below the lists :

List I (Metallic oxide)

A. Uranium oxide

B. Cuprous oxide

C. Cobalt oxide

D. Chromium oxide

List II (Colour imparted to glass)

1. Red

2. Blue

3. Green

4. Yellow

Code :

A B C D

(a) 4 1 2 3

(b) 3 2 1 4

(d) 3 1 2 4

(a) 4 1 2 3

(b) 3 2 1 4

(d) 3 1 2 4

Answer: (a) A-4, B-1, C-2, D-3

Explanation: A. Uranium oxide → yellow/green fluorescent glass = 4 (Yellow). B. Cuprous oxide (Cu₂O) → red glass = 1 (Red). C. Cobalt oxide (CoO) → blue glass = 2 (Blue). D. Chromium oxide (Cr₂O₃) → green glass = 3 (Green). Code (a). Concept Tested: Metal oxides and colours imparted to glass

NDA 2011-I

Q. 18. Which one among the following is the main ingredient in cement ?

(a) Gypsum

(b) Lime stone

(d) Ash

Answer: (b) Lime stone

Explanation: Limestone (CaCO₃) is the main raw material for cement. When limestone is heated (calcined), it gives CaO (quicklime), which reacts with silica and alumina from clay to form the calcium silicates and aluminates that make up Portland cement. Concept Tested: Main ingredient in cement – limestone

Q. 19. Glass is actually :

(a) a crystalline solid.

(b) an ionic solid.

(d) a vitrified liquid.

Answer: (d) a vitrified liquid.

Explanation: Glass is a supercooled liquid (also called a vitrified liquid or amorphous solid). It does not have a long-range crystalline structure. It has no definite melting point – it softens gradually over a range of temperatures. Concept Tested: Nature of glass – supercooled liquid (amorphous, vitrified)

Q. 20. Which of the statements about glass are correct ?

1. Glass is a super-cooled liquid having infinite viscosity

2. Violet coloured glass is obtained by adding MnO₂

3. Glass is a man made silicate

4. Glass is a crystalline substance

Select the correct answer using the code given below :

(a) 1, 2 and 4

(b) 2, 3 and 4

(d) 1 and 3 only

Answer: (c) 1, 2 and 3

Explanation: Statement 1: Correct – glass is a supercooled liquid with very high viscosity. Statement 2: Correct – MnO₂ gives violet/purple colour to glass. Statement 3: Correct – glass is a synthetic (man-made) silicate material. Statement 4: Incorrect – glass is NOT crystalline; it is amorphous. Concept Tested: Properties of glass – amorphous, coloured by metal oxides, man-made silicate

★ JOVIK Exam Insight: MnO₂ = violet glass. CuO = blue/green. Cr₂O₃ = green. CoO = blue. Fe₂O₃ = yellow/brown. Gold = ruby red.

NDA 2009-II

Q. 21. Match List-I with List-II and select the correct answer using the code given below the Lists:

List-I (Material)

A. Cement

B. Glass

C. Ink

D. Soap

List-II (Important Ingredient)

1. Sodium salt of fatty acids

2. Carbon black

3. Silica in the form of quartz

4. Aluminates and silicates of calcium

Code :

A B C D

(a) 4 3 2 1

(b) 1 2 3 4

(d) 4 2 3 1

(a) 4 3 2 1

(b) 1 2 3 4

(d) 4 2 3 1

Answer: (a) A-4, B-3, C-2, D-1

Explanation: A. Cement: aluminates and silicates of calcium = 4. B. Glass: silica in the form of quartz = 3. C. Ink: carbon black (for black ink) = 2. D. Soap: sodium salt of fatty acids = 1. Code (a): A-4, B-3, C-2, D-1. Concept Tested: Ingredients of cement, glass, ink and soap

NDA 2009-I

Q. 22. Match List I with List II and select the correct answer using the code given below the lists:

List I (Substance)

A. Glass

B. Soap

C. Paper

D. Cement

List II (Raw Material)

1. Fat and caustic alkali

2. Cellulose fibre and gelatin

3. Silicates of calcium and aluminium

4. Silica

Code :

A B C D

(a) 3 2 1 4

(b) 4 2 1 3

(d) 4 1 2 3

(a) 3 2 1 4

(b) 4 2 1 3

(d) 4 1 2 3

Answer: (d) A-4, B-1, C-2, D-3

Explanation: A. Glass: raw material includes silica (SiO₂) = 4. B. Soap: made from fat and caustic alkali (NaOH/KOH) = 1. C. Paper: made from cellulose fibre and gelatin = 2. D. Cement: made from silicates of calcium and aluminium (limestone + clay) = 3. Code (d): A-4, B-1, C-2, D-3. Concept Tested: Raw materials for glass, soap, paper and cement