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Carbon & Its Compounds — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Carbon & Its Compounds MCQs with step-by-step solutions covering Allotropes of Carbon, Hydrocarbons, Functional Groups, Carbon Cycle. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — 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.
Q2 — 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.
Q3 — Hydrocarbons · easy · theory
Which of the following is the simplest hydrocarbon?
A. Ethane (C2H6)
B. Methane (CH4) ✓ Correct
C. Ethyne (C2H2)
D. Ethene (C2H4)
Solution: Methane, CH4, has just one carbon atom and is the simplest of all hydrocarbons. The others each contain two carbon atoms.
Q4 — Hydrocarbons · easy · theory
Hydrocarbons are compounds made up of only which two elements?
A. Carbon and nitrogen
B. Carbon and hydrogen ✓ Correct
C. Hydrogen and oxygen
D. Carbon and oxygen
Solution: By definition a hydrocarbon contains only carbon and hydrogen. Adding other elements such as oxygen would give a different class of compound.
Q5 — Functional Groups · easy · theory
Which functional group is present in alcohols?
A. -CHO (aldehyde)
B. -COOH (carboxyl)
C. -OH (hydroxyl) ✓ Correct
D. >C=O (carbonyl)
Solution: Alcohols are characterised by the hydroxyl group, -OH, as in ethanol (C2H5OH). The other groups define acids, aldehydes and ketones.
Q6 — Functional Groups · easy · theory
Vinegar owes its sourness to acetic acid. Which functional group does acetic acid contain?
A. >C=O (ketone)
B. -COOH (carboxyl) ✓ Correct
C. -OH (hydroxyl)
D. -CHO (aldehyde)
Solution: Acetic acid (ethanoic acid, CH3COOH) contains the carboxyl group -COOH, which is responsible for its acidic, sour nature.
Q7 — Carbon Cycle · easy · theory
Which process removes carbon dioxide from the atmosphere?
A. Combustion
B. Respiration
C. Photosynthesis ✓ Correct
D. Decomposition
Solution: During photosynthesis green plants take in carbon dioxide and convert it into food, removing CO2 from the air. Respiration, combustion and decomposition all release CO2.
Q8 — 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.
Q9 — 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.
Q10 — 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.
Q11 — 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.
Q12 — Hydrocarbons · hard · theory
Hydrocarbons that contain only single bonds between carbon atoms are called:
A. saturated (alkanes) ✓ Correct
B. unsaturated (alkenes)
C. unsaturated (alkynes)
D. aromatic
Solution: Saturated hydrocarbons (alkanes) have only C–C single bonds.
Q13 — Hydrocarbons · hard · theory
A hydrocarbon containing a carbon–carbon double bond is:
A. propane (C₃H₈)
B. ethane (C₂H₆)
C. methane (CH₄)
D. ethene (C₂H₄) ✓ Correct
Solution: Ethene has a C=C double bond, making it an unsaturated alkene.
Q14 — Hydrocarbons · hard · theory
Ethyne (acetylene), used in welding torches, contains a carbon–carbon:
A. double bond
B. triple bond ✓ Correct
C. single bond
D. ionic bond
Solution: Ethyne (C₂H₂) has a C≡C triple bond.
Q15 — Functional Groups · hard · theory
The functional group present in carboxylic acids like acetic acid is:
A. –OH (hydroxyl)
B. –NH₂ (amine)
C. –CHO (aldehyde)
D. –COOH (carboxyl) ✓ Correct
Solution: Carboxylic acids contain the carboxyl group, –COOH.
Q16 — Functional Groups · hard · theory
The compound ethanoic acid contains which functional group?
A. hydroxyl (–OH)
B. ketone (>C=O)
C. aldehyde (–CHO)
D. carboxyl (–COOH) ✓ Correct
Solution: Ethanoic acid (acetic acid) has the carboxyl group, –COOH.
Q17 — Functional Groups · hard · theory
The functional group –CHO is characteristic of:
A. alcohols
B. aldehydes ✓ Correct
C. ketones
D. carboxylic acids
Solution: The –CHO group is the aldehyde functional group.
Q18 — Carbon Cycle · hard · theory
Which processes ADD carbon dioxide to the atmosphere?
A. Respiration and combustion of fuels ✓ Correct
B. Photosynthesis only
C. Filtration
D. Condensation and melting
Solution: Respiration by living things and the burning of fuels both release CO₂.
Q19 — Carbon Cycle · hard · theory
The increasing concentration of carbon dioxide in the atmosphere due to burning of fossil fuels leads to:
A. more rainfall everywhere
B. a decrease in temperature
C. thicker ozone layer
D. global warming (enhanced greenhouse effect) ✓ Correct
Solution: Extra CO₂ traps more heat, raising global temperatures (global warming).
Q20 — Carbon Cycle · hard · theory
The decomposition of dead plants and animals by microbes returns carbon to the environment mainly as:
A. oxygen
B. pure carbon
C. nitrogen gas
D. carbon dioxide ✓ Correct
Solution: Decomposers break down organic matter, releasing CO₂ back into the cycle.
Q21 — 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.
Q22 — Hydrocarbons · hard · numerical
An alkene has the general formula CnH2n. A particular alkene has a molecular mass of 42 (take C = 12, H = 1). Its molecular formula is:
A. C4H8
B. C3H8
C. C2H4
D. C3H6 ✓ Correct
Solution: For CnH2n the mass is 12n + 2n = 14n. Setting 14n = 42 gives n = 3, so the formula is C3H6 (propene), whose mass is 3(12) + 6 = 42. C3H8 is rejected because it is an alkane, not an alkene.
Q23 — Functional Groups · hard · theory
Assertion (A): Ethanoic acid turns blue litmus red. Reason (R): It contains the carboxyl (-COOH) group, which makes it behave as an acid. Choose the correct option.
A. Both A and R are true, and R correctly explains A ✓ Correct
B. A is true but R is false
C. Both A and R are true, but R does not explain A
D. A is false but R is true
Solution: Ethanoic acid is acidic and does turn blue litmus red (A is true). This acidity arises from the carboxyl group -COOH (R is true), and that group is exactly why it is acidic, so R correctly explains A.
Q24 — Functional Groups · hard · theory
The molecular formula C2H6O can represent two different compounds (isomers) that have different functional groups. Which pair are they?
A. Methanol and methanal
B. Ethanoic acid and ethanol
C. Ethene and ethyne
D. Ethanol (-OH group) and dimethyl ether (-O- linkage) ✓ Correct
Solution: Both ethanol (CH3CH2OH) and dimethyl ether (CH3OCH3) have the formula C2H6O but different functional groups (a hydroxyl versus an ether linkage), making them functional isomers. The other pairs have different molecular formulas.
Q25 — Carbon Cycle · hard · theory
Carbon locked inside dead organisms slowly turned into fossil fuels such as coal and petroleum over millions of years. Burning these fuels today upsets the carbon cycle mainly because it:
A. releases stored carbon back into the air far faster than natural processes can remove it ✓ Correct
B. stops photosynthesis from happening anywhere on Earth
C. permanently destroys all the oxygen in the atmosphere
D. creates brand-new carbon atoms that did not exist before
Solution: Fossil fuels stored carbon slowly over millions of years, but burning them returns that carbon to the atmosphere as CO2 in a very short time. Nature cannot reabsorb it fast enough, so CO2 builds up and the natural balance is disturbed. Carbon atoms are recycled, not newly created.
Q26 — Carbon Cycle · hard · theory
Assertion (A): The total amount of carbon on Earth stays almost constant. Reason (R): Carbon is continuously recycled between the atmosphere, living organisms, oceans and rocks. Choose the correct option.
A. Both A and R are true, but R does not explain A
B. A is false but R is true
C. Both A and R are true, and R correctly explains A ✓ Correct
D. A is true but R is false
Solution: The total carbon on Earth stays nearly constant (A is true) precisely because carbon keeps moving in a cycle between air, living things, oceans and rocks without being created or destroyed (R is true and explains A).
Q27 — 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).
Q28 — 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.
Q29 — 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.
Q30 — 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.