Which one of the following materials is not an allotrope of carbon?
- (a)Diamond
- (b)Graphene
- (c)Fly ash
- (d)Fullerene
Correct — C, Fly ash. Allotropes of carbon are different structural forms of the pure element carbon — diamond, graphene and fullerene all fit this. Fly ash is not an allotrope of carbon: it is the fine powdery residue left after burning coal in thermal power plants, a mixture of oxides (mainly silica, alumina and iron oxide) with only some unburnt carbon, so it is not a pure form of the element.
- (a)Diamond — Diamond is a genuine allotrope of carbon — each carbon atom is bonded tetrahedrally to four others, giving the hardest natural substance — so it is not the exception.
- (b)Graphene — Graphene is a single one-atom-thick sheet of carbon atoms, a true allotrope of carbon, so it is not the answer.
- (d)Fullerene — Fullerene (for example C₆₀, 'buckminsterfullerene') is a molecular allotrope of pure carbon, so it too is a form of the element.
Allotropes are different structural forms of the same element, in which the atoms are bonded in different arrangements. Carbon has several — diamond (3-D tetrahedral network), graphite (stacked sheets), graphene (a single sheet), fullerenes (closed cages) and carbon nanotubes — all made of pure carbon but with very different properties.
The trap is that fly ash comes from burning coal, which is carbon-rich, so it 'sounds' carbon-related. But fly ash is an oxide-rich combustion ash, not elemental carbon, so it is the odd one out. The other three are all recognised pure-carbon allotropes.
- Allotropes of carbon include diamond, graphite, graphene, fullerene and carbon nanotubes.
- Diamond is the hardest natural substance; graphite is soft, slippery and conducts electricity.
- Graphene is a single-atom-thick carbon sheet — among the thinnest and strongest materials known.
- Fly ash is the powdery residue from coal combustion (mainly silica and alumina) and is used in cement, not a carbon allotrope.
Fly ash is coal-burning residue, not a pure form of carbon — the odd one out the question wants.
- Assuming anything derived from coal counts as a form of carbon.
- Confusing fly ash with graphite, charcoal or coke.
Asked as 'which is not an allotrope of carbon?' or by matching each allotrope to a property such as hardness, conductivity or thinness.
Graphene is frequently in news recently. What is its importance? 1. It is a two-dimensional material and has good electrical conductivity. 2. It is one of the thinnest but strongest materials tested so far. 3. It is entirely made of silicon and has high optical transparency. 4. It can be used as conducting electrodes required for touch screens, LCDs and organic LEDs. Which of the statements given above are correct?
- (a) 1 and 2 only
- (b) 3 and 4 only
- (c) 1, 2 and 4 only
- (d) 1, 2, 3 and 4
Answer(c) 1, 2 and 4 only — graphene is a carbon (not silicon) allotrope, so statement 3 is wrong.
Same concept — graphene as an allotrope of carbon; its option 3 (made of silicon) mirrors the trap here of mistaking a non-carbon material for a carbon form.
Match List-I with List-II and select the correct answer using the code given below the Lists: List-I (Allotrope of Carbon) A. Graphite B. Diamond C. Fullerene D. Graphene List-II (Property) 1. Thinnest and strongest material 2. Hardest natural substance 3. Very light and strong material 4. Soft and slippery material Code:
- (a) A-4, B-2, C-3, D-1
- (b) A-4, B-3, C-2, D-1
- (c) A-1, B-3, C-2, D-4
- (d) A-1, B-2, C-3, D-4
Answer(a) A-4, B-2, C-3, D-1
Same concept — the allotropes of carbon and their properties, directly matching the diamond/graphene/fullerene forms listed in this question.
- practice — not a real PYQ
Which one of the following is NOT an allotrope of carbon?
- (a)Graphite
- (b)Diamond
- (c)Quartz
- (d)Fullerene
Answer(c) Quartz — it is silicon dioxide (SiO₂), not a form of carbon.
- practice — not a real PYQ
The hardest known natural allotrope of carbon is
- (a)graphite
- (b)graphene
- (c)diamond
- (d)fullerene
Answer(c) diamond — its rigid 3-D tetrahedral network makes it the hardest natural substance.