Matter: Elements, Compounds and Mixtures – NDA Chemistry PYQs

Solve NDA Chemistry previous-year questions on Matter: Elements, Compounds and Mixtures with detailed solutions and explanations.

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

NDA 2026-II

Q. 1. Consider the following statements :

I. A solution of iodine in ethanol known as ‘tincture of iodine’ is a heterogeneous mixture.

II. A suspension is a heterogeneous mixture and its particles scatter a beam of light passing through it, making its path visible.

III. A colloidal solution, although it appears homogeneous, is a heterogeneous mixture.

Which of the statements given above are correct ?

(a) I and II only

(b) II and III only

(d) I, II and III

Answer: (b) II and III only

Explanation:
Statement I is NOT correct: tincture of iodine (iodine dissolved in ethanol) is a true solution – a homogeneous mixture, not heterogeneous.
Statement II is correct: a suspension is heterogeneous and its larger particles scatter light, making the path of the beam visible.
Statement III is correct: a colloid appears homogeneous but is actually heterogeneous at the microscopic level. So statements II and III are correct.
Concept Tested: Classification of mixtures -true solution, colloid and suspension

★ JOVIK Exam Insight: Tincture of iodine is a true solution (solute fully dissolved), not a colloid or suspension. NDA 2026-II used it to test whether students know the exact classification of a pharmacy-familiar substance.

Q. 2. Consider the following pairs :

Example of Colloid Type of Colloid

I. Cloud Aerosol

II. Mud Sol

III. Milk Emulsion

IV. Rubber Foam

How many of the pairs given above are correctly matched ?

(a) One

(b) Two

(d) All four

Answer: (c) Three

Explanation:
Pair I -Cloud is an aerosol (liquid water droplets dispersed in gas/air): CORRECT.
Pair II – Mud is a sol (solid particles dispersed in liquid water): CORRECT.
Pair III – Milk is an emulsion (liquid fat droplets dispersed in liquid water): CORRECT.
Pair IV – Rubber is a solid sol or gel, NOT a foam (foam = gas dispersed in liquid or solid): NOT CORRECT.
Three pairs are correctly matched.
Concept Tested: Types of colloidal systems – aerosol, sol, emulsion, foam

★ JOVIK Exam Insight: This question tests precise colloid type nomenclature. The key distinction: foam has gas as the dispersed phase; rubber is a solid sol where solid particles are dispersed in a solid medium.

NDA 2026-I

Q. 3. Consider the following statements :

I. A colloid and a suspension are heterogeneous mixtures.

II. Colloids can be separated from the mixture by the process of centrifugation.

III. Particles of colloids and suspensions can be seen by naked eye.

IV. The aqueous solution of copper sulphate does not show Tyndall effect; however, the mixture of milk and water shows Tyndall effect.

Which of the statements given above is/are correct?

(a) I only

(b) II and III only

(d) I, II and IV

Answer: (d) I, II and IV

Explanation: Statement I is correct: both colloids and suspensions are heterogeneous mixtures. Statement II is correct: centrifugation is used to separate colloidal particles. Statement III is NOT correct: colloidal particles cannot be seen by the naked eye (they are 1–1000 nm); only suspension particles (>1000 nm) may be visible. Statement IV is correct: a true solution (copper sulphate) does not show the Tyndall effect, while a colloid (milk in water) does. Concept Tested: Comparison of solutions, colloids and suspensions – Tyndall effect and particle size

Q. 4. A non-volatile solid solute may be separated from a solution by which of the following processes?

I. Evaporation

II. Crystallization

Select the correct answer using the code given below.

(a) I only

(b) II only

(d) Neither I nor II

Answer: (c) Both I and II

Explanation: Both evaporation and crystallization can separate a non-volatile solid solute from a solution. In evaporation, the solvent is driven off by heat, leaving the solute behind. In crystallization, the solution is cooled slowly so the solute comes out as pure crystals. Both are valid separation methods for this purpose. Concept Tested: Separation of solute from solution – evaporation and crystallization

NDA 2025-II

Q. 5. Which one of the following is NOT a heterogeneous mixture?

(a) Sulphur in carbon disulphide

(b) Mixture of sugar and salt crystals

(d) Sulphur in water

Answer: (a) Sulphur in carbon disulphide

Explanation: Sulphur dissolves completely in carbon disulphide (CS₂) to form a true homogeneous solution – the mixture is uniform throughout and shows the same composition everywhere. A mixture of sugar and salt crystals is heterogeneous (solid-solid). Sandy water is heterogeneous (solid in liquid, particles visible). Sulphur in water is heterogeneous (sulphur does not dissolve in water). So (a) is the only homogeneous mixture.
Concept Tested: Homogeneous vs heterogeneous mixtures – sulphur in CS₂

Q. 6. Match List I with List II and select the answer using the code given below the Lists:

List I (Element)

A. Phosphorus

B. Nitrogen

C. Neon

D. Sulphur

List II (Atomicity)

1. 2

2. 1

3. 8

4. 4

Code :

A B C D

(a) 4 1 2 3

(b) 4 2 1 3

(d) 3 1 2 4

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

Explanation:
Phosphorus exists as P₄ – atomicity 4.
Nitrogen exists as N₂ – atomicity 2.
Neon is a noble gas that exists as single atoms – atomicity 1.
Sulphur exists as S₈ – atomicity 8.
Therefore: A→4, B→1, C→2, D→3. This matches option (a).
Concept Tested: Atomicity of elements – P₄, N₂, Ne, S₈

★ JOVIK Exam Insight: Atomicity is frequently tested in NDA. The key values to remember: Noble gases = 1; H₂, N₂, O₂, F₂, Cl₂ = 2; P₄ = 4; S₈ = 8.

NDA 2025-I

Q. 7. Which one of the following statements about a compound is NOT correct?

(a) A compound is a substance composed of two or more elements, chemically combined in a fixed proportion

(b) Properties of a compound are different from its constituent elements

(d) The constituents of a compound can be separated only by chemical or electrochemical reactions

Answer: (c) A compound is an impure substance

Explanation: A compound is a pure substance – it has a definite and fixed chemical composition throughout. Options (a), (b) and (d) are all true statements about compounds. Option (c) is NOT correct – a compound is by definition a pure substance, not an impure one. Concept Tested: Definition and properties of compounds – pure substance classification

NDA 2024-II

Q. 8. Which one among the following separation techniques is used for blood tests in diagnostic laboratories?

(a) Filtration

(b) Chromatography

(d) Crystallization

Answer: (c) Centrifugation

Explanation: Blood is a colloidal mixture of plasma and cells. In diagnostic laboratories, centrifugation is used to separate blood into its components – red blood cells, white blood cells and plasma – by spinning the sample at high speed. The denser components settle at the bottom. Filtration, chromatography and crystallization are not used for blood separation. Concept Tested: Centrifugation – separation of blood components

Q. 9. Which one among the following elements is polyatomic?

(a) Phosphorus

(b) Sulphur

(d) Aluminium

Answer: Editorial Review Required

Explanation: Both Phosphorus and Sulphur are polyatomic elements. Phosphorus exists as P₄ (tetraatomic – four atoms per molecule). Sulphur exists as S₈ (octaatomic – eight atoms per molecule). Both (a) and (b) are therefore correct by definition. Chlorine is diatomic (Cl₂). Aluminium is monatomic in its standard metallic form. Because two options are defensible, the official NDA 2024-II answer key must be verified before a single confident answer is assigned. Concept Tested: Atomicity of elements – polyatomic: P₄ and S₈

NDA 2023-II

Q. 10. Match List I with List II and select the correct answer using the code given below the Lists :

List I (Process)

A. Separation of acetone and water from their mixture

B. Separation of water and kerosene oil from their mixture

C. Separation of cream from milk

D. Separation of pigments from plant extract

List II (Separation method)

1. Chromatography

2. Centrifugation

3. Distillation

4. Separating Funnel

Code :

A B C D

(a) 3 2 4 1

(b) 4 2 1 3

(d) 4 1 2 3

Answer: (c) 3 4 2 1

Explanation: A (acetone and water – miscible liquids) → 3. Distillation. B (water and kerosene – immiscible liquids) → 4. Separating Funnel. C (cream from milk – lighter phase from colloidal system) → 2. Centrifugation. D (pigments from plant extract – complex mixture of similar compounds) → 1. Chromatography. Code (c): A-3, B-4, C-2, D-1 is correct. Concept Tested: Matching separation techniques to appropriate mixtures

★ JOVIK Exam Insight: NDA uses matching questions on separation methods regularly. The four key methods to link: distillation (miscible liquids), separating funnel (immiscible liquids), centrifugation (cream/colloidal systems), chromatography (similar compounds or plant pigments).

Q. 11. Which among the following is NOT true with respect to colloidal solution ?

(a) Particles are uniformly distributed throughout the solution

(b) Colloidal solution is homogenous in nature

(d) They do not settle down when kept undisturbed

Answer: (b) Colloidal solution is homogenous in nature

Explanation: A colloidal solution appears homogeneous to the naked eye but is actually heterogeneous in nature – the dispersed particles are larger than in a true solution. Options (a), (c) and (d) are all true: colloidal particles are evenly distributed, they show the Tyndall effect, and they do not settle spontaneously. Option (b) is NOT true. Concept Tested: Properties of colloidal solutions – homogeneous vs heterogeneous

Q. 12. Kerosene and petrol mixture can be best separated by

(a) Sublimation

(b) Separating funnel

(d) Compressing and cooling

Answer: (c) Fractional distillation

Explanation: Kerosene and petrol are both liquid petroleum fractions that are miscible with each other. They have different but close boiling points (petrol: approximately 40–70 °C; kerosene: approximately 150–275 °C). Fractional distillation separates miscible liquids with different boiling points. A separating funnel works only for immiscible liquids; sublimation is for solids. Concept Tested: Fractional distillation of petroleum fractions

NDA 2023-I

Q. 13. Which one of the following apparatus is used for separating benzene and water mixture ?

(a) Round bottom flask

(b) Conical flask

(d) Dean and Stark apparatus

Answer: Editorial Review Required

Explanation: This question requires editorial caution. Benzene and water are immiscible liquids – they do not mix and form two distinct layers. At the standard Class 11–12 / NDA level, the separating funnel (c) is the conventional answer for separating any two immiscible liquids. However, benzene and water also form an azeotrope at approximately 69.3 °C, and the Dean and Stark apparatus (d) is specifically used in laboratories to continuously remove water from a reaction mixture via azeotropic distillation. Whether the intended answer is (c) or (d) depends on the level of convention the question-setter had in mind. The authoritative NDA 2023-I official key must be verified before publication. Concept Tested: Separation of immiscible liquids – separating funnel vs Dean and Stark apparatus

NDA 2022-I

Q. 14. Which one of the following is not a solution?

(a) Alloy

(b) Milk

(d) Sugar

Answer: Editorial Review Required

Explanation: This question has an answer ambiguity. An alloy is a solid solution – for example, brass is a homogeneous mixture of copper and zinc. Air is a gaseous solution – a homogeneous mixture of nitrogen, oxygen and other gases. Milk is a colloid – fat droplets are dispersed in water, making it a heterogeneous mixture, not a true solution. Sugar by itself is a pure solid compound (C₁₂H₂₂O₁₁), not a solution at all. Both milk (b) and sugar (d) can therefore be defended as “not a solution” depending on the classification convention used. The authoritative NDA 2022-I key must be verified before a confident answer is assigned. Concept Tested: Types of mixtures – true solutions, colloidal systems and pure substances

NDA 2021-II

Q. 15. Which one of the following methods can be used to separate anthracene from a mixture of salt and anthracene?

(a) Distillation

(b) Sublimation

(d) Chromatography

Answer: (b) Sublimation

Explanation: Anthracene is a polycyclic aromatic compound that sublimes – it converts directly from solid to vapour on heating. Common salt (NaCl) does not sublime. Heating the mixture causes the anthracene to sublime; the vapour is collected and cooled to recover pure anthracene, leaving NaCl behind. Concept Tested: Separation by sublimation – anthracene

Q. 16. Tyndall effect is a phenomenon of

(a) scattering of light by the colloidal particles.

(b) refraction of light by the colloidal particles.

(d) refraction of light by dust particles.

Answer: (a) scattering of light by the colloidal particles.

Explanation: The Tyndall effect is the scattering of a beam of light by the particles in a colloid. When light passes through a colloidal solution, the colloidal particles are large enough to scatter the light, making the beam visible. True solutions (like salt in water) do not show the Tyndall effect because their particles are too small to scatter light. Concept Tested: Tyndall effect – light scattering in colloids

★ JOVIK Exam Insight: The Tyndall effect is tested multiple times in NDA. It is always scattering, never refraction or dispersion. A colloid shows it; a true solution does not.

NDA 2020

Q. 17. Which one of the following is not a monatomic element?

(a) Copper

(b) Helium

(d) Barium

Answer: (c) Iodine

Explanation: Iodine exists naturally as a diatomic molecule (I₂), not as single atoms. Copper, helium and barium all exist as individual atoms in their standard state, making them monatomic. Iodine is therefore the correct answer here. Concept Tested: Atomicity of elements – diatomic vs monatomic

★ JOVIK Exam Insight: This question is identical to NDA 2019-II Q89. Its repetition confirms that atomicity of elements is a reliable NDA exam concept.

NDA 2019-II

Q. 18. Which one of the following substances is not a mixture?

(a) Tin

(b) Sea water

(d) Air

Answer: (a) Tin

Explanation: Tin (Sn) is a pure metallic element with atomic number 50. It has a fixed composition and uniform properties. Sea water is a mixture of water, salts and dissolved gases. Soil is a heterogeneous mixture of minerals, organic matter and water. Air is a mixture of gases. Only tin is a pure element, not a mixture. Concept Tested: Pure elements distinguished from mixtures

Q. 19. Which one of the following is not a monatomic element?

(a) Copper

(b) Helium

(d) Barium

Answer: (c) Iodine

Explanation: Monatomic elements exist as single atoms. Noble gases (like helium) are monatomic. Most metals (copper, barium) are also monatomic in their standard state. Iodine (I₂) is a diatomic element – it exists as a molecule of two iodine atoms bonded together. So iodine is not monatomic. Concept Tested: Atomicity of elements – monatomic vs diatomic

★ JOVIK Exam Insight: This exact question appeared again in NDA 2020, making it a repeated question. Iodine, along with F₂, Cl₂, Br₂, O₂, N₂, H₂, are the diatomic non-metals to remember.

NDA 2019-I

Q. 20. Which one of the following substances is NOT a mixture?

(a) Ice

(b) Ice-cream

(d) Honey

Answer: (a) Ice

Explanation: Ice is pure water in solid form (H₂O). It has a fixed chemical composition and is a pure compound, not a mixture. Ice-cream is a mixture of milk solids, fats, sugar and flavourings. Air is a mixture of gases. Honey is a complex mixture of sugars, water and other substances. Only ice is a pure substance. Concept Tested: Identifying pure substances – ice as a pure compound

NDA 2018-II

Q. 21. Which one of the following is a heterogeneous mixture?

(a) Hydrochloric acid

(b) Vinegar

(d) Soda water

Answer: (c) Milk

Explanation: Milk is a colloidal mixture – fat globules are dispersed in water, making it heterogeneous at the microscopic level (even though it appears uniform to the eye). Hydrochloric acid is a true solution of HCl in water (homogeneous). Vinegar is a solution of acetic acid in water (homogeneous). Soda water is a solution of CO₂ in water (homogeneous). Only milk qualifies as heterogeneous. Concept Tested: Homogeneous vs heterogeneous mixtures – everyday examples

NDA 2017-I

Q. 22. A homogeneous mixture contains two liquids. How are they separated?

(a) By filtration

(b) By evaporation

(d) By condensation

Answer: (c) By distillation

Explanation: When two liquids form a homogeneous (miscible) mixture, they cannot be separated by filtration, evaporation alone, or condensation alone. Distillation makes use of the difference in boiling points of the two liquids to separate them. The liquid with the lower boiling point vaporises first, is condensed, and collected separately. Concept Tested: Separation of miscible liquid mixtures – distillation

Q. 23. 20 g of common salt is dissolved in 180 g of water. What is the mass percentage of the salt in the solution?

(a) 5%

(b) 9%

(d) 15%

Answer: (c) 10%

Explanation: Mass percentage = (mass of solute / mass of solution) × 100. Mass of solution = 20 g (salt) + 180 g (water) = 200 g. Mass percentage = (20 / 200) × 100 = 10%. Option (c) is correct. Concept Tested: Calculation of mass percentage of a solution

★ JOVIK Exam Insight: NDA occasionally includes a simple numerical calculation on concentration. The formula is: mass% = (mass of solute / total mass of solution) × 100. Total mass = solute + solvent.

NDA 2016-II

Q. 24. Emulsion is known as a

(a) colloidal solution of substances having different physical states

(b) true solution

(d) colloidal solution of two liquids

Answer: (d) colloidal solution of two liquids

Explanation: An emulsion is a colloidal system where one liquid is dispersed in another liquid. Common examples include milk (fat droplets in water) and mayonnaise. Both the dispersed phase and the dispersion medium are liquids. This distinguishes an emulsion from other colloid types such as aerosols (liquid in gas) or gels (solid in liquid). Concept Tested: Types of colloidal systems – emulsion

NDA 2013-II

Q. 25. A mixture of sodium chloride and naphthalene can be separated by

(a) extraction with hot water

(b) extraction with cold water

(d) steam distillation

Answer: (c) sublimation

Explanation: Naphthalene is a sublimable substance – it turns directly from solid to vapour on heating. Sodium chloride does not sublime. On heating the mixture, naphthalene sublimes and is collected separately, leaving behind pure NaCl. Sublimation is the cleanest and most direct method for this separation. Concept Tested: Separation by sublimation – naphthalene and NaCl

★ JOVIK Exam Insight: NDA repeatedly tests sublimable substances: naphthalene, NH₄Cl, iodine, camphor, anthracene. Recognise the sublimable component and the answer is always sublimation.

NDA 2012-II

Q. 26. Air is

(a) always a compound

(b) always a mixture

(d) a mixture in industrial zones

Answer: (b) always a mixture

Explanation: Air is always a mixture of gases – mainly nitrogen, oxygen, argon and carbon dioxide. Its composition can vary from place to place. There is no fixed chemical ratio between its components. Pollution or clean zones do not change this fundamental nature. Air is never a compound. Concept Tested: Nature of air as a mixture

NDA 2011-II

Q. 27. Which one among the following is not a mixture ?

(a) Graphite

(b) Glass

(d) Steel

Answer: (a) Graphite

Explanation: Graphite is a pure allotrope of carbon – it is a pure element, not a mixture. Glass is an amorphous mixture of silicates. Brass is an alloy (mixture) of copper and zinc. Steel is an alloy (mixture) of iron and carbon. Only graphite is a pure substance. Concept Tested: Identifying pure elements among alloys and mixtures

★ JOVIK Exam Insight: Graphite appeared as the correct “element” answer in NDA 2009-I as well. NDA consistently tests carbon allotropes as pure elements distinct from alloys.

NDA 2011-I

Q. 28. A student by chance mixed acetone with alcohol. This mixture of acetone and alcohol can be separated by :

(a) filtration.

(b) separating funnel.

(d) fractional distillation.

Answer: (d) fractional distillation.

Explanation: Acetone and alcohol are both liquids that are miscible with each other. Filtration removes solids, not liquids. A separating funnel separates immiscible liquids. Fractional crystallization separates solids. Only fractional distillation can separate two miscible liquids with different boiling points. Acetone boils at about 56 °C and ethanol at about 78 °C, so fractional distillation is used. Concept Tested: Separation of miscible liquid mixtures by fractional distillation

NDA 2010-II

Q. 29. A mixture containing SiO₂, NaCl and NH₄Cl is taken for separating the constituents. The suitable steps required for this are :

(a) Sublimation-dissolution-filtration-crystallization

(b) Dissolution-filtration-crystallization-distillation

(d) Dissolution-distillation-decomposition-evaporation

Answer: (a) Sublimation-dissolution-filtration-crystallization

Explanation: NH₄Cl sublimes on heating, so sublimation is done first to remove it from the mixture. The remaining SiO₂ and NaCl are then dissolved in water. SiO₂ does not dissolve, so filtration separates it. NaCl remains in solution and is recovered by crystallization. This four-step sequence matches option (a). Concept Tested: Separation of three-component mixtures using sublimation, filtration and crystallization

★ JOVIK Exam Insight: This type of multi-step separation question is a favourite in NDA. Always identify the sublimable component (NH₄Cl, iodine, naphthalene) first – it is always removed in step one.

Q. 30. Iodized salt is a :

(a) mixture of potassium iodide and common salt

(b) mixture of molecular iodine and common salt

(d) compound formed by combination of molecular iodine and common salt

Answer: (a) mixture of potassium iodide and common salt

Explanation: Iodized salt is made by adding a small quantity of potassium iodide (KI) or potassium iodate (KIO₃) to common salt (NaCl). No chemical reaction takes place between them. Their individual properties are retained. So iodized salt is a mixture, not a compound. Concept Tested: Mixture vs compound – iodized salt as an example

Q. 31. Which one among the following statements regarding the properties of mixtures and compounds is not correct?

(a) A mixture shows the properties of its constituents but the properties of a compound are entirely different from its constituents

(b) A mixture may be homogeneous or heterogeneous but a compound is a homogeneous substance

(c) The constituents of a mixture can be separated by physical methods but those of a compound can not be separated by physical method

(d) Energy is either absorbed or evolved during the preparation of a mixture but not in the preparation of a compound

Answer: (d) Energy is either absorbed or evolved during the preparation of a mixture but not in the preparation of a compound

Explanation: This statement reverses the correct fact. It is the formation of a compound that involves energy change – bonds are formed or broken during a chemical reaction. The formation of a mixture generally does not involve a significant energy change. Options (a), (b) and (c) are all correct distinctions between mixtures and compounds. Concept Tested: Differences between mixtures and compounds

★ JOVIK Exam Insight: NDA uses “not correct” or “incorrect” phrasing frequently. Read each option against the core rule: compound formation involves energy change; mixing usually does not.

NDA 2009-II

Q. 32. Which one of the following is not a mixture?

(a) Air

(b) Mercury

(d) Cement

Answer: (b) Mercury

Explanation: Mercury is a pure metallic element (Hg) – it has a fixed composition and uniform properties throughout. Air is a mixture of gases. Milk is a colloidal mixture of fats, proteins and water. Cement is a mixture of calcium silicates, aluminates and other compounds. Only mercury is a pure substance, not a mixture. Concept Tested: Distinguishing pure substances from mixtures

NDA 2009-I

Q. 33. Which among the following is an element?

(a) Alumina

(b) Brass

(d) Silica

Answer: (c) Graphite

Explanation: Graphite is a pure form of carbon, which is an element. Alumina (Al₂O₃) is a compound of aluminium and oxygen. Brass is an alloy (mixture) of copper and zinc. Silica (SiO₂) is a compound of silicon and oxygen. Only graphite consists of a single type of atom. Concept Tested: Elements, compounds and mixtures – identification

★ JOVIK Exam Insight: NDA regularly tests whether students can identify an element among compounds and mixtures. Remember: alloys are mixtures, not compounds.