Chapter 4: Carbon and its Compounds

VVI questions — the ones the board asked most (20)

1. Q1Long answer5 marksAsked: 2021

   Write the method of preparing methane gas in the laboratory and its chemical reaction with chlorine.

   

   Medha Ma’am

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   Model answer · preparation of methane, reaction with chlorine

   1. 1.Methane gas is obtained in the laboratory by heating sodium acetate with soda lime. Sodium acetate (CH3COONa) is mixed with soda lime, which is a mixture of sodium hydroxide (NaOH) and calcium oxide (CaO), and the mixture is heated strongly in a test tube. Methane gas is evolved and can be collected over water.1 mark
   2. 2.The chemical equation for the reaction is: CH3COONa + NaOH --CaO/heat--> CH4 + Na2CO3 Here sodium acetate reacts with sodium hydroxide in the presence of calcium oxide (CaO) on heating to give methane (CH4) gas along with sodium carbonate (Na2CO3).1.5 marks
   3. 3.Methane reacts with chlorine in the presence of sunlight to form chloromethane. This is a substitution reaction because one type of atom or a group of atoms takes the place of another; chlorine replaces the hydrogen atoms of methane one by one in a very fast reaction when exposed to sunlight.1 mark
   4. 4.The chemical equation for the reaction is: CH4 + Cl2 --sunlight--> CH3Cl + HCl Here methane reacts with chlorine in the presence of sunlight to form chloromethane (CH3Cl) and hydrogen chloride (HCl) gas.1.5 marks

   Diagram: Draw a test tube clamped on a stand containing a mixture of sodium acetate and soda lime being heated over a burner, with delivery tube passing into a gas jar collected over water; label the test tube as "CH3COONa + soda lime (NaOH + CaO)", the burner as "heat", the delivery tube, and the gas jar as "CH4 gas collected over water".

   • Write the full equation CH3COONa + NaOH --CaO--> CH4 + Na2CO3 exactly, showing CaO as the condition.
   • State clearly that the reaction of methane with chlorine is called a substitution reaction and that it occurs in the presence of sunlight.
   • Write the equation CH4 + Cl2 --sunlight--> CH3Cl + HCl with sunlight written as the condition above the arrow.

   Marks split from a structure derived from past papers (checked twice); not Bihar Board’s official scheme

2. Q2Long answer5 marksAsked: 2024

   Write down the laboratory method of preparation of methane and its chemical reaction with chlorine.

   

   Medha Ma’am

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   Hear it from Medha Ma’am · 85 s

   Model answer · preparation of methane, reaction with chlorine

   1. 1.A mixture of sodium acetate and soda lime (NaOH + CaO) is heated in a test tube to give methane gas.1 mark
   2. 2.CH₃COONa + NaOH → (CaO, heat) CH₄ + Na₂CO₃1 mark
   3. 3.Methane is insoluble in water, so it is collected in a gas jar by downward displacement of water.1 mark
   4. 4.Diagram: a test tube with the mixture, clamped to a stand and heated; a delivery tube leading to an inverted gas jar over water in a trough — test tube, stand, delivery tube and gas jar labelled.1 mark
   5. 5.In sunlight methane reacts with chlorine to give methyl chloride and hydrogen chloride: CH₄ + Cl₂ → (light) CH₃Cl + HCl — a substitution reaction.1 mark

   Marks split from a structure derived from past papers (checked twice); not Bihar Board’s official scheme

3. Q3Long answer5 marksAsked: 2023

   What do you understand by saponification? Explain. How is it different from esterification?

   

   Medha Ma’am

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   Hear it from Medha Ma’am · 90 s

   Model answer · saponification vs esterification

   1. 1.Saponification is the process of forming soap and glycerol by heating esters of higher fatty acids with sodium hydroxide or potassium hydroxide. When an ester is treated with sodium hydroxide, which is an alkali, the ester is converted back into alcohol and the sodium salt of the carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.2 marks
   2. 2.The chemical equation for the saponification reaction is CH3COOC2H5 + NaOH → CH3COONa + C2H5OH.1 mark
   3. 3.Esterification is the process in which the reaction between a carboxylic acid and an alcohol results in the formation of an ester and water. Ethanoic acid reacts with absolute ethanol in the presence of an acid catalyst to give an ester. Esters are sweet-smelling substances and are used in making perfumes and as flavouring agents.1 mark
   4. 4.Saponification is the reverse process of esterification. This is because esterification involves the formation of an ester from a carboxylic acid and an alcohol, while saponification involves the decomposition of the ester back into alcohol and the sodium salt of the carboxylic acid (soap).1 mark

   • Begin with the full definition of saponification using the words 'soap and glycerol' and 'sodium hydroxide or potassium hydroxide'.
   • Write the saponification equation CH3COOC2H5 + NaOH → CH3COONa + C2H5OH exactly as given, each term correctly placed.

   Marks split from a structure derived from past papers (checked twice); not Bihar Board’s official scheme

4. Q4Long answer5 marksAsked: 2022

   What are hydrocarbons ? What are it types ?

   How the model answer begins

   1. Compounds formed by the combination of hydrogen and carbon are called hydrocarbons.

   The full answer from Medha Ma’am →
5. Q5Short answer2 marksAsked: 2021

   Write the structural formula of ethyl alcohol.

   How the model answer begins

   1. The structural formula of ethyl alcohol (ethanol) is CH₃–CH₂–OH.

   The full answer from Medha Ma’am →
6. Q6Short answer2 marksAsked: 2021

   Write the structural formulae of butanone and ethanoic acid.

   How the model answer begins

   1. The structural formula of butanone is CH3-CH2-CO-CH3.

   The full answer from Medha Ma’am →
7. Q7Short answer2 marksAsked: 2024

   Why does carbon mainly form covalent compounds ?

   How the model answer begins

   1. Carbon mainly forms covalent compounds because carbon has four electrons in its outermost shell and needs to gain or lose four electrons to attain noble gas configuration. Instead of forming C4– by gaining four…

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8. Q8Short answer2 marksAsked: 2025

   Why have detergents replaced soap ?

   How the model answer begins

   1. Detergents have replaced soap because detergents can produce lather even in hard water. This is because the charged ends of detergents do not form insoluble precipitates with the calcium and magnesium ions present in…

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9. Q9Short answer2 marksAsked: 2025

   What are aliphatic compounds?

   How the model answer begins

   1. Organic compounds in which carbon atoms are arranged in an open chain are called aliphatic compounds.

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10. Q10Short answer2 marksAsked: 2025

    What do you understand by homologous series? Write with examples.

    How the model answer begins

    1. A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. In such a series, successive compounds differ by a –CH2– unit, so any two consecutive…

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11. Q11Short answer2 marksAsked: 2026

    Why are carbon and its compounds used as fuel ?

    How the model answer begins

    1. Carbon and its compounds are used as fuel because they release a large amount of heat and light on combustion. Carbon burns in oxygen to give carbon dioxide along with the release of heat and light: C + O2 → CO2 + heat…

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12. Q12Short answer2 marksAsked: 2026

    What is isomerism ? Give one example.

    How the model answer begins

    1. Compounds having the same molecular formula but different structures are called isomers and this phenomenon is known as isomerism.

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13. Q13Short answer2 marksAsked: 2025

    Why is inert gas filled in an electric bulb?

    How the model answer begins

    1. Inert gas is filled in the electric bulb to protect the tungsten filament from oxidation.

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14. Q14Short answer2 marksAsked: 2023

    Show the electron dot structure of carbon dioxide (CO2).

    How the model answer begins

    1. Carbon has 4 electrons and each oxygen 6 electrons in the outermost shell, shown as dots in the structure.

    The full answer from Medha Ma’am →
15. Q15Short answer2 marksAsked: 2023

    What is a detergent? Give an example.

    How the model answer begins

    1. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they…

    The full answer from Medha Ma’am →
16. Q16Short answer2 marksAsked: 2022

    Write the structural formulae and names of the isomers of pentane.

    How the model answer begins

    1. Pentane has the molecular formula C5H12 and it has three structural isomers having identical molecular formula but different structures. These isomers are named n-pentane, iso-pentane and neo-pentane.

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17. Q17Short answer2 marksAsked: 2022

    What are hydrocarbons? What are its types?

    How the model answer begins

    1. Compounds formed by the combination of hydrogen and carbon are called hydrocarbons.

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18. Q18Short answer2 marksAsked: 2022

    What are the effects of drinking alcohol on the body?

    How the model answer begins

    1. When large quantities of ethanol are consumed, it tends to slow metabolic processes and to depress the central nervous system. This results in lack of coordination, mental confusion, drowsiness, lowering of the normal…

    The full answer from Medha Ma’am →
19. Q19Short answer2 marksAsked: 2022

    What is soap?

20. Q20Short answer2 marksAsked: 2022

    What is a covalent bond? Give two examples of it.

    How the model answer begins

    1. Such bonds which are formed by the sharing of an electron pair between two atoms are known as covalent bonds. In the formation of this bond, the shared pair of electrons belongs to the outer shells of both the atoms and…

    The full answer from Medha Ma’am →

2 more questions of this chapter, each with its model answer, in the AskMedha app.

Objective questions with the board’s key (10)

1. 1. Bihar Board 2026

   The molecular formula of ethyl alcohol is

   • (A) CH3OH
   • (B) C2H5OH ✓
   • (C) C2H6OH
   • (D) C2H2OH

   Answer: (B)

2. 2. Bihar Board 2026

   The molecular formula of benzene is

   • (A) CH4
   • (B) C2H2
   • (C) C6H6 ✓
   • (D) C2H4

   Answer: (C)

3. 3. Bihar Board 2026

   Which of the following pairs is isomeric ?

   • (A) C2H6 and C6H6
   • (B) C5H10 and C5H12
   • (C) C2H5OH and CH3OCH3 ✓
   • (D) CH4 and C2H6

   Answer: (C)

4. 4. Bihar Board 2026

   The IUPAC name of acetic acid is

   • (A) Ethanoic acid ✓
   • (B) Methanoic acid
   • (C) Propanone
   • (D) Aldehyde

   Answer: (A)

5. 5. Bihar Board 2026

   Which element is not present in alcohol ?

   • (A) Carbon
   • (B) Oxygen
   • (C) Hydrogen
   • (D) Nitrogen ✓

   Answer: (D)

6. 6. Bihar Board 2026

   Which of the following is a hydrocarbon ?

   • (A) H2O
   • (B) C4H10 ✓
   • (C) CO2
   • (D) HNO3

   Answer: (B)

7. 7. Bihar Board 2026

   - OH is the functional group of

   • (A) Ketone
   • (B) Alcohol ✓
   • (C) Aldehyde
   • (D) None of these

   Answer: (B)

8. 8. Bihar Board 2026

   How many covalent bonds are there in methane ?

   • (A) 2
   • (B) 4 ✓
   • (C) 6
   • (D) 8

   Answer: (B)

9. 9. Bihar Board 2026

   The shape of C60 Fullerene is similar to which of the following ?

   • (A) Pear
   • (B) Damru
   • (C) Football ✓
   • (D) None of these

   Answer: (C)

10. 10. Bihar Board 2026

    The main component of domestic gas ( LPG ) is

    • (A) Methane
    • (B) Butane ✓
    • (C) Ethane
    • (D) Propane

    Answer: (B)

Questions parents and students ask

How many marks does "Carbon and its Compounds" carry in Bihar Board Class 10 Science?

In the Bihar Board papers of 2021–2026, this chapter carried about 5 marks and about 7 questions a year; by marks it ranks 6 in Science.

Which are the most important (VVI) questions of "Carbon and its Compounds"?

The 20 questions above are from the board’s real papers, each with the years it was asked; the most-asked come first with their full model answers. All 22 written questions of this chapter, with answers, are in the AskMedha app.

Do the answers follow the board’s marking scheme?

BSEB does not publish a marking scheme. Each answer is written point by point on a structure derived from past papers and checked by a second, independent model; it is never called the board’s official scheme.