Buckminster fullerene, which looks like a football, is an allotropic form of
- (a)Phosphorus
- (b)Sulfur
- (c)Carbon
- (d)Tin
Correct — C, Carbon. NCERT Class 10 Science introduces fullerenes as another class of carbon allotropes, and says the first one identified was C-60, which has its carbon atoms arranged in the shape of a football. Its full name honours the American architect Buckminster Fuller, because the closed cage of linked rings looks like his geodesic domes. Sixty carbon atoms sit at the corners of a closed surface built from pentagons and hexagons, exactly the pattern of panels on a football, and every atom in the cage is carbon — which makes carbon the parent element.
- (a)Phosphorus — Phosphorus does have well-known allotropes, including white and red phosphorus, but they are built from small tetrahedral units and extended chains, not from a sixty-atom closed cage. No form of phosphorus is called a fullerene.
- (b)Sulfur — Sulphur also has allotropes, notably the rhombic and monoclinic crystalline forms, and both are made of puckered eight-atom rings rather than a football-shaped cage. Note in passing that this booklet prints the American spelling here while spelling the same element the British way elsewhere in the paper.
- (d)Tin — Tin has allotropes too — the ordinary white metallic form and a brittle grey form it turns into in severe cold — but they are ordinary crystal structures of a metal. Buckminsterfullerene is a molecular cage of a non-metal, and tin forms nothing of the kind.
Allotropes are different structural forms of the same element in the same physical state. Because only the arrangement of the atoms changes, allotropes share the element's chemical properties but can have wildly different physical ones. Carbon is the classic case, with diamond, graphite and the fullerenes all built from nothing but carbon atoms bonded in three quite different ways.
The clue is planted in the question itself — a shape like a football points straight at C-60. Several of the wrong options are elements that genuinely do have allotropes, which is what makes them tempting, so do not settle for the fact that an element has allotropes; ask which element has this allotrope. Keep allotropes separate from isotopes, which are atoms of one element differing in mass number, not in structure.
- NCERT Class 10 Science states that fullerenes are a class of carbon allotropes and that the first one identified was C-60, with its carbon atoms arranged in the shape of a football.
- The molecule is named after the US architect Buckminster Fuller, whose geodesic dome it resembles.
- In diamond each carbon atom is bonded to four others in a rigid three-dimensional structure; in graphite each is bonded to three others in hexagonal planar layers.
- Diamond is the hardest substance known while graphite is soft, slippery and a good conductor of electricity, even though the chemical properties of the two are the same.
All three are pure carbon and differ only in how the atoms are bonded; the football-shaped cage is C-60.
- Confusing an allotrope, which is a different structure of the same element, with an isotope, which is a different mass number.
- Assuming diamond and graphite differ chemically; their chemical properties are the same and only structure and physical properties change.
- Thinking carbon is the only element with allotropes — sulphur, phosphorus and tin have them too.
NDA asks which substance is or is not an allotrope of carbon, or sets diamond against graphite on hardness and conductivity — anchor every answer on the bonding pattern.
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
Same family of carbon structures — graphene is a single hexagonal sheet of carbon and its statement 3, which calls it silicon, fails for exactly the reason fullerene is carbon and not one of the other elements offered here.
Which one of the following materials is not an allotrope of carbon?
- (a) Diamond
- (b) Graphene
- (c) Fly ash
- (d) Fullerene
Answer(c) Fly ash
Lists fullerene among the carbon allotropes explicitly, which is the very fact this question asks for.
Which one of the following statements about diamond and graphite is not correct?
- (a) Diamond has a tetrahedral structure, whereas graphite has a hexagonal planar structure.
- (b) Both physical and chemical properties of diamond and graphite are different.
- (c) Graphite is soft but diamond is hard.
- (d) Graphite is a good conductor of electricity while diamond is not.
Answer(b) Both physical and chemical properties of diamond and graphite are different.
Tests the defining feature of allotropy — same element and same chemistry, different structure and different physical properties.
- practice — not a real PYQ
The C-60 fullerene molecule takes its name from
- (a)the chemist who first synthesised it
- (b)the architect Buckminster Fuller, whose geodesic dome it resembles
- (c)the laboratory in which it was first detected
- (d)the Latin word for sixty
Answer(b) the architect Buckminster Fuller, whose geodesic dome it resembles — the closed cage of pentagons and hexagons looks like his domes, which is how the molecule got its name.
- practice — not a real PYQ
Which one of the following is NOT an allotrope of carbon?
- (a)Graphite
- (b)Diamond
- (c)Fullerene
- (d)Quartz
Answer(d) Quartz — it is crystalline silicon dioxide, not a form of the element carbon at all.