Homologous series and naming: Class 10 practice
Members of a homologous series differ by CH₂ and share a general formula: alkanes CₙH₂ₙ₊₂, alkenes CₙH₂ₙ, alkynes CₙH₂ₙ₋₂. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Covalent bonding of carbon
The idea behind homologous series and naming
Members of a homologous series differ by CH₂ and share a general formula: alkanes CₙH₂ₙ₊₂, alkenes CₙH₂ₙ, alkynes CₙH₂ₙ₋₂. Names use meth-, eth-, prop-, but-, pent-, hex- for 1–6 carbons, with -ane, -ene, -yne, -ol, -al, -one, -oic acid endings.
Step-by-step method
- Count the carbons → root name.
- Identify the family → ending.
- Use the general formula to get the hydrogens.
Worked example 1 (Basic)
Name the alkane with 6 carbon atoms and write its formula.
- 6 carbons → "hex"
- Formula C₆H₁₄
- Answer: hexane, C₆H₁₄
Worked example 2 (Standard)
Name the alkyne with 3 carbon atoms and write its formula.
- 3 carbons → "prop"
- Formula C₃H₄
- Answer: propyne, C₃H₄
Worked example 3 (Challenge)
Name the carboxylic acid with 2 carbon atoms and write its formula.
- 2 carbons → "eth"
- Formula CH₃COOH
- Answer: ethanoic acid, CH₃COOH
Common mistakes and misconceptions
- Using CₙH₂ₙ₊₂ for alkenes
- Wrong root for 4 carbons
Practice questions
- (Basic) Name the alkane with 3 carbon atoms and write its formula.
- (Basic) Name the alkane with 5 carbon atoms and write its formula.
- (Standard) Name the alkene with 5 carbon atoms and write its formula.
- (Standard) Name the alkyne with 2 carbon atoms and write its formula.
- (Challenge) Name the carboxylic acid with 4 carbon atoms and write its formula.
- (Challenge) Name the alcohol with 6 carbon atoms and write its formula.
Answer key with full working
- Q1: 3 carbons → "prop" → Formula C₃H₈ → Answer: propane, C₃H₈
- Q2: 5 carbons → "pent" → Formula C₅H₁₂ → Answer: pentane, C₅H₁₂
- Q3: 5 carbons → "pent" → Formula C₅H₁₀ → Answer: pentene, C₅H₁₀
- Q4: 2 carbons → "eth" → Formula C₂H₂ → Answer: ethyne, C₂H₂
- Q5: 4 carbons → "but" → Formula C₃H₇COOH → Answer: butanoic acid, C₃H₇COOH
- Q6: 6 carbons → "hex" → Formula C₆H₁₃OH → Answer: hexanol, C₆H₁₃OH
Syllabus note
This skill is listed under "Carbon and its Compounds" for Class 10 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is homologous series and naming in?
"Carbon and its Compounds", Class 10 Chemistry (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.