Interstitial compounds are those which are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals.
-- NCERT Class 12 Chemistry, Ch. 4, p. 104Interstitial Alloys
8 MCQs9-step worked example
Source: NCERT The d and f Block ElementsOfficial key: NTA-verifiedLast updated: 7 Oct 2026
Try this first
Interstitial compounds of the transition metals are those formed when
- A.two metals with similar radii are blended into a homogeneous solid solution
- B.small atoms like H, C or N are trapped inside the crystal lattices of metals
- C.metal ions bond with ligands through available d orbitals
- D.a metal ion changes its oxidation state during a catalysed reaction
Tap to see the answer
Answer: B. NCERT Class 12 Chemistry, Chapter 4, page 104: interstitial compounds are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals. (This is the same statement that appears as option 4 of NEET 2020 Q147, where it is a correct statement.)
A is wrong: A is wrong because that describes an alloy (page 104), not an interstitial compound.
C is wrong: C is wrong because that describes complex formation, a different property listed just above on page 104.
D is wrong: D is wrong because that describes the catalytic activity explained on page 104, not interstitial compounds.
Interstitial Alloys, explained for NEET
The trap: Interstitial compounds and alloys sit next to each other on one NCERT page, and students blend them. They are different things. In an interstitial compound, small non-metal atoms sit inside a metal's lattice. An alloy is a blend of metals.
Interstitial compounds. NCERT defines them as compounds "formed when small atoms like H, C or N are trapped inside the crystal lattices of metals". They are usually non-stoichiometric and "neither typically ionic nor covalent", for example TiC, Mn₄N, Fe₃H, VH₀.₅₆ and TiH₁.₇. The formulas "do not correspond to any normal oxidation state of the metal". Four characteristics follow (NCERT Class 12 Chemistry, Chapter 4, page 104):
- melting points higher than those of the pure metals;
- very hard (some borides approach diamond);
- metallic conductivity is retained;
- chemically inert.
Alloys. An alloy is "a blend of metals prepared by mixing the components". It may be a homogeneous solid solution in which the atoms of one metal are distributed randomly among the atoms of the other. Such alloys form between atoms whose metallic radii are within about 15 percent of each other. Transition metals have similar radii and other characteristics, so they form alloys readily, and the alloys are hard with often high melting points (page 104).
Examples to hold: chromium, vanadium, tungsten, molybdenum and manganese go into steels and stainless steel. Brass (copper-zinc) and bronze (copper-tin) are alloys of a transition metal with a non-transition metal (page 104).
Watch-out: TiC contains carbon, a non-metal, so it is an interstitial compound. Brass contains only metals, so it is an alloy. Ask what is being added to the metal.
How do you solve a Interstitial Alloys question? A worked example
- 1
Given
Four substances are listed: TiC, brass (copper-zinc), VH₀.₅₆ and bronze (copper-tin).
- 2
Required
Sort each as an interstitial compound or an alloy, and state the test used.
- 3
Concept
An interstitial compound has small H, C or N atoms trapped in a metal lattice. An alloy is a blend of metals (NCERT Class 12 Chemistry, Chapter 4, page 104).
- 4
Formula
Test: does the substance add a non-metal atom (H, C or N) to the metal, or a second metal?
- 5
Substitution
TiC: Ti metal + C atoms. Brass: Cu + Zn. VH₀.₅₆: V metal + H atoms. Bronze: Cu + Sn.
- 6
Calculation
Non-metal added: TiC (C) and VH₀.₅₆ (H), so 2 interstitial compounds. Second metal added: brass (Zn) and bronze (Sn), so 2 alloys. Total 2 + 2 = 4 substances, so none is left unsorted. The counts are counting integers and carry no significant-figure meaning.
- 7
Final answer
Interstitial compounds: TiC and VH₀.₅₆. Alloys: brass and bronze. NCERT lists TiC and VH₀.₅₆ among its interstitial examples and brass and bronze among its alloys (page 104).
- 8
Common trap
Calling TiC an alloy because "Ti is a metal and C is mixed in". The mixing partner is a non-metal that sits in the lattice, so it is an interstitial compound.
- 9
Similar NEET-style question
Classify Mn₄N and a copper-tin blend. (Answer: Mn₄N has N, a small non-metal atom, trapped in the manganese lattice, so it is an interstitial compound; the copper-tin blend mixes two metals, so it is an alloy, bronze. Test result: N added to Mn gives interstitial, Sn added to Cu gives alloy; both are on page 104.)
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Can you answer these Interstitial Alloys MCQs?
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
MCQ 1Easy RecallPractice
Interstitial compounds of the transition metals are those formed when
Show answer and why every option is right or wrong
Answer: B. NCERT Class 12 Chemistry, Chapter 4, page 104: interstitial compounds are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals. (This is the same statement that appears as option 4 of NEET 2020 Q147, where it is a correct statement.)
Why A is wrong: A is wrong because that describes an alloy (page 104), not an interstitial compound.
Why C is wrong: C is wrong because that describes complex formation, a different property listed just above on page 104.
Why D is wrong: D is wrong because that describes the catalytic activity explained on page 104, not interstitial compounds.
MCQ 2Easy RecallPractice
Which of the following is given by NCERT as an example of an interstitial compound?
Show answer and why every option is right or wrong
Answer: D. NCERT Class 12 Chemistry, Chapter 4, page 104 lists TiC, Mn₄N, Fe₃H, VH₀.₅₆ and TiH₁.₇ as interstitial compounds.
Why A is wrong: A is wrong because brass is copper-zinc, an alloy of a transition metal with a non-transition metal (page 104).
Why B is wrong: B is wrong because bronze is copper-tin, also an alloy (page 104).
Why C is wrong: C is wrong because stainless steel is a ferrous alloy made with metals such as chromium and manganese (page 104).
MCQ 3Easy RecallPractice
What does NCERT say about the composition and bonding of interstitial compounds?
Show answer and why every option is right or wrong
Answer: A. NCERT Class 12 Chemistry, Chapter 4, page 104: they "are usually non stoichiometric and are neither typically ionic nor covalent".
Why B is wrong: B is wrong because the formulas (for example VH₀.₅₆ and TiH₁.₇) are non-stoichiometric, and the bonding is not typically ionic (page 104).
Why C is wrong: C is wrong because NCERT says they are neither typically ionic nor covalent (page 104).
Why D is wrong: D is wrong because NCERT says the formulas quoted do not correspond to any normal oxidation state of the metal (page 104).
MCQ 4Direct ApplicationPractice
Which set of properties describes the interstitial compounds of the transition metals?
Show answer and why every option is right or wrong
Answer: C. NCERT Class 12 Chemistry, Chapter 4, page 104 lists four characteristics: high melting points (higher than pure metals), very hard, metallic conductivity retained, chemically inert.
Why A is wrong: A is wrong because all four properties are reversed; NCERT gives higher melting points, very hard, conducting, inert (page 104).
Why B is wrong: B is wrong because the compounds are very hard, not soft, and are chemically inert, not reactive (page 104).
Why D is wrong: D is wrong because NCERT says they retain metallic conductivity, so they are not insulating (page 104).
MCQ 5Direct ApplicationPractice
Alloys form readily between atoms whose metallic radii are within about what percentage of each other?
Show answer and why every option is right or wrong
Answer: B. NCERT Class 12 Chemistry, Chapter 4, page 104: such alloys are formed by atoms with metallic radii within about 15 percent of each other.
Why A is wrong: A is wrong because 5 percent is narrower than the limit NCERT states (page 104).
Why C is wrong: C is wrong because 30 percent is double the stated limit (page 104).
Why D is wrong: D is wrong because 50 percent is far outside the stated limit (page 104).
MCQ 6Direct ApplicationPractice
Which group of metals does NCERT name as used in the production of a variety of steels and stainless steel?
Show answer and why every option is right or wrong
Answer: A. NCERT Class 12 Chemistry, Chapter 4, page 104: chromium, vanadium, tungsten, molybdenum and manganese are used for a variety of steels and stainless steel.
Why B is wrong: B is wrong because copper, zinc and tin are the metals of brass (copper-zinc) and bronze (copper-tin), not the steel-making group (page 104).
Why C is wrong: C is wrong because the page names transition metals for steels; sodium, potassium and calcium are not named (page 104).
Why D is wrong: D is wrong because hydrogen and carbon are the small atoms of interstitial compounds like TiH₁.₇ and TiC, not alloying metals (page 104).
MCQ 7CalculationPractice
Consider TiH₁.₇ and brass. Which statement is correct?
Show answer and why every option is right or wrong
Answer: D. NCERT Class 12 Chemistry, Chapter 4, page 104: TiH₁.₇ is listed as an interstitial compound (small H atoms trapped in the metal lattice), and brass (copper-zinc) is an alloy, a blend of metals.
Why A is wrong: A is wrong because brass has no small non-metal atoms trapped in a lattice; it is copper blended with zinc (page 104).
Why B is wrong: B is wrong because TiH₁.₇ contains hydrogen, a non-metal, so it is not a blend of metals (page 104).
Why C is wrong: C is wrong because it swaps the two; the hydride is interstitial and brass is the alloy (page 104).
MCQ 8Concept TrapPractice
Why are alloys readily formed by transition metals?
Show answer and why every option is right or wrong
Answer: C. NCERT Class 12 Chemistry, Chapter 4, page 104: "Because of similar radii and other characteristics of transition metals, alloys are readily formed by these metals."
Why A is wrong: A is wrong because fitting into lattice gaps is how small atoms (H, C, N) form interstitial compounds, not why metals blend into alloys (page 104).
Why B is wrong: B is wrong because high ionic charge and d-orbital availability are the page-104 reasons for complex formation, not for alloy formation.
Why D is wrong: D is wrong because chemical inertness is listed for interstitial compounds, and it is not the reason given for alloy formation (page 104).
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What to remember before solving Interstitial Alloys questions
4 NCERT lines
An alloy is a blend of metals prepared by mixing the components. Because of similar radii and other characteristics of transition metals, alloys are readily formed by these metals. The alloys so formed are hard and have often high melting points.
-- NCERT Class 12 Chemistry, Ch. 4, p. 104They are usually non stoichiometric and are neither typically ionic nor covalent, for example, TiC, Mn4N, Fe3H, VH0.56 and TiH1.7, etc. They have high melting points, higher than those of pure metals. They are very hard, some borides approach diamond in hardness. They retain metallic conductivity. They are chemically inert.
-- NCERT Class 12 Chemistry, Ch. 4, p. 104Alloys may be homogeneous solid solutions in which the atoms of one metal are distributed randomly among the atoms of the other. Such alloys are formed by atoms with metallic radii that are within about 15 percent of each other. The best known are ferrous alloys: chromium, vanadium, tungsten, molybdenum and manganese are used for the production of a variety of steels and stainless steel. Alloys of transition metals with non transition metals such as brass (copper-zinc) and bronze (copper-tin), are also of considerable industrial importance.
-- NCERT Class 12 Chemistry, Ch. 4, p. 104Interstitial Alloys: NEET previous year questions (PYQs) with answers
15 questions in The d and f Block Elements
No question in our NEET 2020–2025 set targets this topic directly.
All 15 past-paper questions from The d and f Block Elements →
More in The d and f Block Elements: 3 exam traps and mistakes · 3 formulas · 3 question patterns from its other lessons.
Sources
NCERT refs: Class 12 Chemistry Chapter 4, p.104
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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