Sulphur, Halogens and Noble Gases  – NDA Chemistry PYQs

NDA 2023-I

Q. 1.  Which among the following is the correct arrangement of halogens in the increasing order of their oxidizing nature ?

(a) F, Cl, Br, I

(b) Cl, Br, F, I

(c) Br, I, Cl, F

(d) I, Br, Cl, F

Answer: (d) I, Br, Cl, F

Explanation: Oxidising power of halogens decreases down Group 17: F > Cl > Br > I. So the increasing order is I < Br < Cl < F, which matches option (d). Concept Tested: Oxidising power of halogens – F > Cl > Br > I

★ JOVIK Exam Insight: Oxidising power decreases down the halogen group. F is the strongest oxidising agent of all elements.

NDA 2021-I

Q. 2.  Which one of the following is the chemical formula of Hypobromous acid?

(a) HBrO₄

(b) HOBr

(c) HBr

(d) HBrO₃

Answer: (b) HOBr

Explanation: Hypobromous acid is the bromine oxoacid where Br has oxidation state +1. Its formula is HOBr or HBrO. HBrO₄ is perbromic acid. HBr is hydrobromic acid. HBrO₃ is bromic acid. Concept Tested: Formula of hypobromous acid – HOBr

NDA 2017-II

Q. 3.  The principal use of hydrofluoric acid is

(a) in etching glass

(b) as a bleaching agent

(c) as an extremely strong oxidizing agent

(d) in the preparation of strong organic fluorine compounds

Answer: (a) in etching glass

Explanation: Hydrofluoric acid (HF) reacts with silicon dioxide (SiO₂) in glass: SiO₂ + 4HF → SiF₄ + 2H₂O. This etches glass surfaces, which is its principal industrial use. Concept Tested: HF etching glass – reacts with SiO₂

NDA 2017-I

Q. 4.  Match List I with List II and select the correct answer using the code given below the Lists:

List I (Noble gas)

A. Argon

B. Neon

C. Krypton

D. Xenon

List II (Use)

1. In lights for advertising display

2. Airport landing lights and in light houses

3. Light in photographer’s flash gun

4. In tungsten filament to last longer

Code :

     A  B  C  D

(a)  3  1  2  4

(b)  3  2  1  4

(c)  4  2  1  3

(d)  4  1  2  3

(a)  3  1  2  4

(b)  3  2  1  4

(c)  4  2  1  3

(d)  4  1  2  3

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

Explanation: A. Argon: used in tungsten filament bulbs to prevent oxidation = 4. B. Neon: used in neon advertising signs (glow discharge) = 1. C. Krypton: used in airport landing lights and lighthouses = 2. D. Xenon: used in photographer’s flash guns = 3. Code (d): A-4, B-1, C-2, D-3. Concept Tested: Uses of noble gases – Ar, Ne, Kr, Xe

★ JOVIK Exam Insight: Noble gas uses to remember: Ar = light bulbs. Ne = advertising signs. Kr = airport/lighthouses. Xe = flash guns. He = balloons/diving.

Q. 5.  Radon is

(a) an inert gas

(b) an artificial fibre

(c) an explosive

(d) a metal

Answer: (a) an inert gas

Explanation: Radon (Rn) is a noble gas (Group 18) – it is inert and radioactive. It is the heaviest noble gas. It is naturally produced from the decay of radium. Concept Tested: Radon – noble gas classification

NDA 2014-I

Q. 6.  Which of the following is correct regarding the reaction of fluorine with water? 2F₂(g) + 2H₂O(l) → 4H⁺(aq) + 4F⁻(aq) + O₂(g)

(a) Fluorine is oxidized to F⁻

(b) Water is oxidized to O₂

(c) Water is reduced to H⁺

(d) Oxidation state of fluorine does not change

Answer: (b) Water is oxidized to O₂

Explanation: In 2F₂ + 2H₂O → 4H⁺ + 4F⁻ + O₂: Fluorine goes from 0 to −1 (reduced). Water/oxygen goes from −2 (in H₂O) to 0 (in O₂) – oxidised. So water is oxidised to O₂. This is unusual because F₂ is the strongest oxidising agent. Concept Tested: Fluorine reacting with water – water is oxidised to O₂

NDA 2013-II

Q. 7.  The presence of sulphur in gunpowder

(a)  decreases the ignition temperature.

(b)  increases the final temperature.

(c)  increases explosiveness of the gunpowder.

(d)  makes the powder smokeless.

Answer: (a) decreases the ignition temperature.

Explanation: Sulphur lowers the ignition temperature of gunpowder, making it easier to ignite. Gunpowder is a mixture of KNO₃ (oxidiser), charcoal (fuel) and sulphur (to lower ignition point). It does not make powder smokeless – that is a property of modern cordite. Concept Tested: Role of sulphur in gunpowder – lowers ignition temperature

NDA 2011-I

Q. 8.  A student heated some sulphur in a spatula and collected the gas ‘X’. Which one among the following is correct about ‘X’ ?

(a) X is SO₂ and it turns moist litmus to blue

(b) X is SO₃ and it turns moist litmus to red

(c) X is SO₂ and it turns moist litmus to red

(d) X is SO₃ and it turns dry litmus to blue

Answer: (c) X is SO₂ and it turns moist litmus to red

Explanation: When sulphur burns in air, it produces sulphur dioxide (SO₂): S + O₂ → SO₂. SO₂ dissolves in moist litmus paper to form sulphurous acid, which turns moist red litmus red (it is already red) – actually it turns blue litmus to red, confirming its acidic nature. Concept Tested: Combustion of sulphur – SO₂ is acidic gas

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