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Carbon & Its Compounds — Homi Bhabha Exam Chemistry MCQs with Solutions
Free Homi Bhabha Exam 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 · 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.
Q2 — 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.
Q3 — 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.
Q4 — 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.
Q5 — 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.
Q6 — 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.
Q7 — 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.
Q8 — 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.
Q9 — 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.
Q10 — 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.
Q11 — 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.
Q12 — 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).
Q13 — 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.
Q14 — 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).
Q15 — 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.
Q16 — 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.
Q17 — 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.
Q18 — Hydrocarbons · medium · theory
A compound made up of only carbon and hydrogen is called a:
A. hydrocarbon ✓ Correct
B. carbohydrate
C. carbonate
D. oxide
Solution: Hydrocarbons contain only carbon and hydrogen atoms (e.g. methane, ethane).
Q19 — Hydrocarbons · medium · theory
The simplest hydrocarbon, the main component of natural gas, is:
A. ethene (C₂H₄)
B. methane (CH₄) ✓ Correct
C. ethyne (C₂H₂)
D. ethane (C₂H₆)
Solution: Methane, CH₄, is the simplest hydrocarbon.
Q20 — Hydrocarbons · medium · theory
When a hydrocarbon burns completely in plenty of air, the products are:
A. only carbon
B. carbon monoxide and hydrogen
C. carbon dioxide and water ✓ Correct
D. ammonia and water
Solution: Complete combustion of a hydrocarbon gives CO₂ and H₂O with the release of heat.
Q21 — Hydrocarbons · medium · theory
CNG and LPG, used as fuels, are mainly mixtures of:
A. metal oxides
B. salts
C. acids
D. hydrocarbons ✓ Correct
Solution: CNG (mostly methane) and LPG (propane/butane) are hydrocarbon fuels.
Q22 — Functional Groups · medium · theory
An atom or group of atoms that gives characteristic properties to an organic compound is called a:
A. noble group
B. functional group ✓ Correct
C. periodic group
D. radical group
Solution: The functional group determines the chemical behaviour of an organic compound.
Q23 — Functional Groups · medium · theory
The functional group present in alcohols (such as ethanol) is:
A. –CO– (ketone)
B. –COOH (carboxyl)
C. –CHO (aldehyde)
D. –OH (hydroxyl) ✓ Correct
Solution: Alcohols contain the hydroxyl group, –OH.
Q24 — Functional Groups · medium · theory
Ethanol (an alcohol) is commonly used:
A. in alcoholic drinks and as a sanitiser ✓ Correct
B. as a fertiliser
C. to make cement
D. as a fuel gas for cooking
Solution: Ethanol is used in beverages, sanitisers and as a solvent/fuel additive.
Q25 — Functional Groups · medium · theory
Vinegar, used in cooking, is a dilute solution of:
A. sulphuric acid
B. hydrochloric acid
C. sodium hydroxide
D. acetic acid (ethanoic acid) ✓ Correct
Solution: Vinegar is about 5–8% acetic (ethanoic) acid in water.
Q26 — Carbon Cycle · medium · theory
The carbon cycle describes the continuous exchange of carbon among the atmosphere, plants, animals and:
A. the soil and oceans ✓ Correct
B. outer space
C. the Sun
D. the Moon
Solution: Carbon circulates among air, living things, soil and oceans in the carbon cycle.
Q27 — Carbon Cycle · medium · theory
The process by which green plants remove carbon dioxide from the atmosphere is:
A. combustion
B. photosynthesis ✓ Correct
C. decomposition
D. respiration
Solution: During photosynthesis, plants take in CO₂ to make food, removing it from the air.
Q28 — Carbon Cycle · medium · theory
Fossil fuels such as coal and petroleum were formed from:
A. sea salt
B. melted rocks
C. the remains of dead plants and animals over millions of years ✓ Correct
D. volcanic lava
Solution: Fossil fuels formed from buried remains of ancient organisms under heat and pressure over ages.
Q29 — Carbon Cycle · medium · theory
The gas released back into the air by both plants and animals during respiration is:
A. carbon dioxide ✓ Correct
B. nitrogen
C. hydrogen
D. oxygen
Solution: Respiration uses oxygen and releases carbon dioxide.
Q30 — Carbon Cycle · medium · theory
Green plants play a key role in the carbon cycle because they:
A. produce fossil fuels directly
B. absorb nitrogen from air
C. fix atmospheric carbon dioxide into food ✓ Correct
D. release carbon dioxide only
Solution: Plants convert atmospheric CO₂ into carbohydrates through photosynthesis, fixing carbon.