Chapter 4: Carbon and Its Compounds Previous Year Questions – Class 10 CBSE Science
Introduction
The chapter Carbon and Its Compounds is one of the
most crucial topics for Class 10 Science under the CBSE syllabus. Carbon’s
unique bonding ability, its multiple allotropic forms, the huge range of
organic compounds it forms — all of these make the chapter rich in concept and
question-types. Many board questions repeatedly cover topics like catenation of
carbon, homologous series, functional groups, basic vs complex organic
reactions (substitution, addition, esterification, saponification), and
distinguishing properties of carbon compounds. Multiple PYQs (Previous Year
Questions) clearly show what is frequently asked. For example:
- “Why
are covalent compounds poor conductors of electricity?” appeared in 2008.
- “What
are the two properties of carbon which lead to a very large number of
carbon compounds?” (AI 2011)
- “Explain
why carbon can neither form C⁴⁺ nor C⁴⁻ but forms covalent bonds.” (2020)
In this article you will find a comprehensive question bank
grouped by type (MCQ, Very Short Answer, Short Answer, Long Answer, Case-Study)
with reference to the year the question appeared (where available). Solve these
to strengthen your concept clarity and board readiness.
Multiple Choice Questions
- C₃H₈
belongs to homologous series of
a) Alkynes
b) Alkenes
c) Alkanes
d) Cycloalkanes → Answer: c) Alkanes - Which
of the following will undergo an addition reaction?
a) CH₄ b) C₃H₈ c) C₂H₆ d) C₂H₄ → Answer: d) C₂H₄ - In a
diamond each carbon atom is bonded to four other carbon atoms to form
a) A hexagonal array
b) A rigid three-dimensional structure
c) A structure in the shape of a football
d) A structure of a ring → Answer: b) A rigid three-dimensional structure - Which
allotrope of carbon is a good conductor of heat and electricity?
a) Diamond b) Graphite c) Charcoal d) None of these → Answer: b) Graphite - Why
don’t other elements of group-14 exhibit catenation like carbon? (2020)
a) Due to larger size and weaker bond energy
b) Because they are metals
c) They form ionic compounds
d) They only form single bonds → Answer: a) Due to larger size and weaker bond energy
Very Short Answer Questions (10–20 words)
- What
is functional group? (2020)
Ans: A specific atom/group of atoms in molecule responsible for characteristic reactions. - Define
homologous series. (2020)
Ans: A family of compounds with same functional group, successive members differ by –CH₂–. - Write
general formula of alkynes. (Foreign 2015)
Ans: CₙH₂ₙ₋₂. - Name
the reaction where hydrogen adds to an unsaturated hydrocarbon.
Ans: Hydrogenation (addition reaction). - Why
are covalent compounds generally poor conductors of electricity? (AI 2018)
Ans: Because they don’t form ions; electrons are not free to move.
Short Answer Questions (≈ 50-70 words)
Q1. State two properties of carbon leading to large
number of carbon compounds. (AI 2011)
Ans: Carbon has tetravalency (can form four covalent bonds) and
catenation (can form chains, branches, rings of C–C bonds). These two features
allow it to form millions of compounds, unlike other group 14 elements whose
bond energies drop down the group.
Q2. What are esters? Write one use. (Delhi 2014)
Ans: Esters are compounds formed by reaction of alcohol with a
carboxylic acid, often pleasant-smelling. Eg: Ethyl ethanoate (CH₃COOCH₂CH₃).
Use: used in making perfumes and artificial flavours.
Q3. Explain substitution vs addition reaction with
one example each. (2020)
Ans: Substitution: hydrogen atom in saturated hydrocarbon replaced by
other atom (e.g., CH₄ + Cl₂ → CH₃Cl + HCl). Addition: atoms add across
unsaturated bond (e.g., C₂H₄ + H₂ → C₂H₆).
Long Answer Questions (≈ 100 words)
Q1. Explain why carbon cannot form C⁴⁺ or C⁴⁻, but
forms covalent bonds. Why are other group-14 elements not very catenating?
(2020)
Ans: Carbon's small size and high ionisation energy make formation of
C⁴⁺ or C⁴⁻ ions highly unfavourable. Instead it forms stable covalent bonds by
sharing electrons. Additionally, C–C bond energy is high, enabling chain
formation (catenation). Other group-14 elements have larger size and weaker
element-element bonds, so their catenation ability drops. Also, the lower
overlap causes weaker bonds and fewer stable compounds, hence fewer compounds
than carbon.
Q2. Write the structure and name of the second member
of alcohol series. Explain saponification reaction and give its use. (Foreign
2012)
Ans: Second member of alcohols: Ethanol (C₂H₅OH, structure CH₃CH₂OH).
Saponification is the reaction where an ester reacts with a base (usually NaOH)
to form soap (sodium salt of fatty acid) and glycerol (or alcohol). Use: Soap
manufacturing.
Case-Study / Competency Questions
CSQ. A compound ‘X’ has molecular formula C₂H₆O. On reacting with sodium metal it evolves gas ‘Y’ which burns with pop sound. On heating ‘X’ with concentrated H₂SO₄ at 443 K it gives unsaturated compound ‘Z’. Identify X, Y, Z. Write equations and role of H₂SO₄. (2018)
Ans: X = Ethanol (C₂H₅OH). Reaction with Na: 2C₂H₅OH + 2Na → 2C₂H₅ONa +
H₂ (Y = H₂). On heating: C₂H₅OH → C₂H₄ (Z = ethene) + H₂O (conc. H₂SO₄ acts as
dehydrating agent).
PYQs with years (selected)
- Why
do covalent compounds have low melting & boiling points? (CBSE AI
2008)
- What
are two properties of carbon which lead to very large number of carbon
compounds? (AI 2011)
- In a
molecule C₄H₁₀, how many covalent bonds? (AI 2015)
- Distinguish
between esterification and saponification with equations. (AI 2017)
- Define
homologous series. Write general formula of alkenes and alkynes. (AI 2014)
Preparation Tips for Board Exam
- Focus
on definitions: functional group, homologous series, catenation.
- Practice
drawing structures of first members of each series (alkane, alkene,
alkyne).
- Memorise
general formulas:
- Alkanes:
CₙH₂ₙ₊₂
- Alkenes:
CₙH₂ₙ
- Alkynes:
CₙH₂ₙ₋₂
- Practice
reaction-types: substitution, addition, esterification, saponification.
- Solve
at least 10–15 PYQs from years above; they help understanding pattern and
repetition.
Summary
Chapter 4 of CBSE Class 10 Science deals with the versatility of carbon — its allotropic forms, bonding, organic chemistry fundamentals (hydrocarbons, functional groups, homologous series, important reactions). Past year questions trend shows recurring themes: properties of carbon compounds, reaction-types, naming and structure of compounds, application in daily life. The question bank above (MCQ, very short, short, long and case-study) with year reference provides a rigorous revision framework.
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