Allotropes of Carbon — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Allotropes of Carbon MCQs with step-by-step solutions (13 questions). Part of Carbon & Its Compounds. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Allotropes of Carbon · medium · theory
Different physical forms of the same element, such as diamond and graphite, are called:
A. allotropes ✓ Correct
B. isotopes
C. compounds
D. isomers
Solution: Allotropes are different structural forms of the same element (both are pure carbon).
Q2 — Allotropes of Carbon · medium · theory
The hardest allotrope of carbon is:
A. diamond ✓ Correct
B. charcoal
C. graphite
D. coke
Solution: Diamond has a rigid 3-D network, making it the hardest known natural substance.
Q3 — Allotropes of Carbon · hard · theory
Which allotrope of carbon conducts electricity?
A. Diamond
B. Coke
C. Graphite ✓ Correct
D. Charcoal
Solution: Graphite has free electrons in its layered structure and conducts electricity, unlike diamond.
Q4 — Allotropes of Carbon · hard · theory
Graphite is used as a lubricant and in pencil leads because it is:
A. soft and slippery (layered structure) ✓ Correct
B. a good insulator
C. a gas
D. extremely hard
Solution: Graphite's layers slide over one another, making it soft, slippery and useful as a lubricant.
Q5 — Allotropes of Carbon · medium · theory
Diamond is used for cutting and drilling because it is:
A. very soft
B. slippery
C. extremely hard ✓ Correct
D. a good conductor
Solution: The hardness of diamond makes it ideal for cutting glass and drilling rocks.
Q6 — Allotropes of Carbon · hard · theory
The spherical (football-shaped) allotrope of carbon containing 60 carbon atoms is:
A. graphite
B. coke
C. Buckminsterfullerene (C₆₀) ✓ Correct
D. diamond
Solution: C₆₀, or Buckminsterfullerene, is a cage-like molecular allotrope of carbon.
Q7 — Allotropes of Carbon · medium · theory
Both diamond and graphite are made up of only the element:
A. carbon ✓ Correct
B. oxygen
C. silicon
D. sulphur
Solution: Despite their different properties, both are pure carbon.
Q8 — Allotropes of Carbon · hard · theory
In diamond, each carbon atom is bonded to ______ other carbon atoms, giving a rigid structure:
A. four ✓ Correct
B. three
C. two
D. six
Solution: Each carbon in diamond forms four strong covalent bonds in a tetrahedral arrangement.
Q9 — Allotropes of Carbon · easy · theory
Which allotrope of carbon is the hardest naturally occurring substance known?
A. Graphite
B. Charcoal
C. Coke
D. Diamond ✓ Correct
Solution: In diamond every carbon is joined to four others in a rigid three-dimensional network, making it the hardest natural substance. Graphite, charcoal and coke are far softer.
Q10 — Allotropes of Carbon · easy · theory
In the structure of graphite, each carbon atom is directly bonded to how many other carbon atoms?
A. 2
B. 6
C. 3 ✓ Correct
D. 4
Solution: Each carbon in graphite forms bonds with three neighbours in flat sheets, using only three of its four valence electrons. The fourth electron is left free, which is why graphite conducts electricity.
Q11 — Allotropes of Carbon · medium · theory
Graphite conducts electricity but diamond does not. The best explanation is that in graphite:
A. the carbon atoms are lighter than those in diamond
B. it contains dissolved metal that carries the current
C. one valence electron per carbon is free to move, while in diamond all four are locked in bonds ✓ Correct
D. it is softer than diamond, so current passes easily
Solution: In graphite each carbon uses only three electrons for bonding, leaving one delocalised electron per atom free to move and carry current. In diamond all four valence electrons are held in bonds, so there are no free electrons and it acts as an insulator.
Q12 — Allotropes of Carbon · medium · numerical
A diamond and a piece of graphite contain the same number of carbon atoms (so equal mass). If the density of diamond is 3.5 g/cm³ and of graphite is 2.2 g/cm³, the ratio of their volumes (diamond : graphite) is closest to:
A. 1 : 1
B. 7 : 11
C. 35 : 22
D. 22 : 35 ✓ Correct
Solution: Equal atoms means equal mass, and volume = mass ÷ density, so volume is inversely proportional to density. Ratio = (1/3.5) : (1/2.2) = 2.2 : 3.5 = 22 : 35. Diamond, being denser, has the smaller volume.
Q13 — Allotropes of Carbon · hard · theory
Which of the following statements about the allotropes of carbon is INCORRECT?
A. Graphite is the hardest allotrope and is therefore set in jewellery ✓ Correct
B. Diamond is very hard and is used in cutting and drilling tools
C. Graphite conducts electricity and is used to make electrodes
D. Buckminsterfullerene (C60) is a hollow cage-like molecule of 60 carbon atoms
Solution: Graphite is soft and slippery, not hard, and is not used in jewellery; that description fits diamond. The other three statements are all correct, so the incorrect statement is the one about graphite being the hardest allotrope.