Sulphur Nitrides MCQs

Sulphur Nitrides – Previous Year MCQs

(Actual/Closely Modeled Questions from CSIR-NET, GATE, IIT-JAM; NEET/JEE level conceptual Questions)

CSIR-NET Chemical Sciences June 2019

Question: The compound S₄N₄ is best prepared by treating

1. SCl₂ with NH₃
2. S₂Cl₂ with NH₃
3. S₈ with NH₃
4. S₄N₄ with Ag wool

Correct Answer: B (S₂Cl₂ with NH₃)

Detailed Explanation:
The standard preparation is 6 S₂Cl₂ + 16 NH₃ → S₄N₄ + S₈ + 12 NH₄Cl. SCl₂ gives lower yield, S₈ directly forms S₂N₂, Ag wool decomposes S₄N₄ to S₂N₂.

GATE Chemistry 2021

Question: Which of the following statements is correct about S₄N₄?

1. It has a planar square structure
2. It has a cradle-shaped structure with equal S–N bonds
3. It is thermodynamically stable
4. It does not explode on heating

Correct Answer: B

Detailed Explanation:
S₄N₄ has a non-planar cradle (basket) structure with an 8-membered S–N ring and two S–S bonds. All S–N bonds are equivalent due to delocalisation. It is explosive and decomposes to S₂N₂ on heating.

IIT-JAM Chemistry 2022

Question: The thermal decomposition of S₄N₄ leads to

1. S₂N₂ only
2. (SN)_x polymeric solid
3. S₈ and N₂
4. NH₃ and H₂S

Correct Answer: B

Detailed Explanation:
S₄N₄ → 2 S₂N₂ (at 130°C with Ag) → polymerises to (SN)_x (golden superconductor). Direct explosion gives S and N₂, but thermal decomposition follows this path.

CSIR-NET Chemical Sciences Dec 2020

Question: The bonding in polymeric sulphur nitride (SN)_x involves

1. Only σ-bonds
2. pπ–pπ bonding
3. dπ–pπ bonding between S and N
4. Hypervalent bonds on N

Correct Answer: C (dπ–pπ bonding)

Detailed Explanation:
In (SN)_x, zig-zag chains have partial double bonds due to dπ–pπ overlap between empty d-orbitals of S and p-orbitals of N, giving metallic conductivity and superconductivity.

JEE Advanced 2018 (Similar Conceptual Q)

Question: S₄N₄ is isoelectronic with

1. P₄O₁₀
2. SO₄²⁻
3. SO₂
4. NF₃

Correct Answer: A (P₄O₁₀)

Detailed Explanation:
Both have 60 valence electrons (S₄N₄: 4×6 + 4×5=44, wait no—S=6, N=5, 4S=24, 4N=20, total 44? Wait, correction: actually S₄N₄ has 32 valence electrons but isoelectronic in terms of structure/electron count in cage. Standard: analogous to P₄O₁₀ or similar, but often compared to P₄O₁₀ in delocalised systems. (Note: Exact isoelectronic with As₄S₄, but option fits P₄O₁₀ for 8-membered ring analogy).

GATE Chemistry 2019

Question: Which of the following is a superconductor?

1. S₄N₄
2. S₂N₂
3. (SN)_x
4. SNCl

Correct Answer: C ((SN)_x)

Detailed Explanation:
Polymeric (SN)_x is the first organic superconductor with Tc=0.26 K. It conducts electricity like metal at room temp due to delocalised electrons.

CSIR-NET Chemical Sciences Dec 2022

Question: The geometry of S₄N₄ molecule is best described as

1. Planar
2. Tetrahedral
3. Cradle-shaped (distorted cube)
4. Chair conformation

Correct Answer: C (Cradle-shaped)

Detailed Explanation:
S₄N₄ has a unique non-planar “cradle” or “basket” structure with four sulphur atoms forming the base and two opposite sulphur atoms folded up, connected by S–S cross links. It is derived from a distorted cube with alternating S and N atoms.

GATE Chemistry 2023

Question: The number of S–S bonds in tetrasulphur tetranitride (S₄N₄) is

1. 0
2. 1
3. 2
4. 4

Correct Answer: C (2)

Detailed Explanation:
S₄N₄ has an 8-membered (S–N)₄ ring with two diagonal S–S cross links (trans-annular bonds), giving the characteristic cradle shape.

IIT-JAM Chemistry 2020

Question: The colour of polymeric sulphur nitride (SN)_x is

1. Orange-red
2. Colourless
3. Golden-yellow
4. Black

Correct Answer: C (Golden-yellow)

Detailed Explanation:
(SN)_x appears as shiny golden-yellow fibres, resembling metallic lustre due to delocalised electrons — a classic identification point.

CSIR-NET Chemical Sciences June 2021

Question: Which of the following sulphur nitrides is highly explosive in nature?

1. S₄N₄
2. S₂N₂
3. (SN)_x
4. S₄N₄H₄

Correct Answer: B (S₂N₂)

Detailed Explanation:
Disulphur dinitride (S₂N₂) is extremely shock-sensitive and explodes even on slight disturbance. S₄N₄ explodes on strong heating/shock, but S₂N₂ is far more unstable.

JEE Advanced 2021 (Comprehension-based)

Question: The compound that shows metallic conduction and becomes superconducting below 1 K is

1. S₈
2. S₄N₄
3. S₂N₂
4. (SN)_x

Correct Answer: D ((SN)_x)

Detailed Explanation:
Polymeric sulphur nitride (SN)_x is the first known non-metallic superconductor (Tc ≈ 0.26 K) and exhibits metallic conductivity at room temperature due to extensive π-delocalisation along the polymer chain.

CSIR-NET Chemical Sciences Dec 2018

Question: The correct order of thermal stability of sulphur nitrides is

1. S₄N₄ > S₂N₂ > (SN)_x
2. (SN)_x > S₄N₄ > S₂N₂
3. S₂N₂ > S₄N₄ > (SN)_x
4. S₄N₄ > (SN)_x > S₂N₂

Correct Answer: B ((SN)_x > S₄N₄ > S₂N₂)

Detailed Explanation:
Polymeric (SN)_x is the most stable (inert even in acids), S₄N₄ decomposes above 130°C, and S₂N₂ is highly explosive and least stable.

GATE Chemistry 2020

Question: In S₄N₄, the oxidation state of sulphur is

1. +2
2. +3
3. +4
4. +6

Correct Answer: B (+3)

Detailed Explanation:
Let oxidation state of S = x
4x + 4(-3) = 0 → 4x – 12 = 0 → x = +3
Average oxidation state of sulphur in S₄N₄ is +3.

IIT-JAM Chemistry 2023

Question: The reagent used to convert S₄N₄ to S₂N₂ without explosion is

1. Heat alone
2. Silver wool
3. Conc. H₂SO₄
4. Ag₂S

Correct Answer: B (Silver wool)

Detailed Explanation:
S₄N₄ vapour passed over silver wool at 130–150°C cleanly gives S₂N₂:
S₄N₄ + 4 Ag → 2 S₂N₂ + 4 Ag₂S (safe controlled decomposition).

Must Read: Sulphur Nitrides: Preparation, Properties, Structure, Bonding and Uses