Which of the following represents the methyl group? | General Science MCQ | Examoogle

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General SciencePrevious Year Paper 2024

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Which of the following represents the methyl group?

$\text{CH}_3$

$\text{CH}$

$\text{CH}_4$

$\text{CH}_2$

Correct Answer

🔬 SC • Science Concept & PrincipleGeneral SciencePrevious Year Paper 2024

Option D

$\text{CH}_2$

Quick Summary:

In a homologous series, successive members differ from each other by a constant unit of $-CH_{2}-$ (methylene group). This addition changes the molecular mass by $14$ atomic mass units (amu).

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🔬SCScience SolutionConcept & Principle

💡 Explanation

In a homologous series, successive members differ from each other by a constant unit of $-CH_{2}-$ (methylene group). This addition changes the molecular mass by $14$ atomic mass units (amu).

💡 Everyday Analogy (Real-World Intuition)

Think of it like adding an extra bogie to a train; every time you add one segment, the train gets longer by the same fixed size.

🧠 Memory Mnemonic / Shortcut Aid

Mnemonic: 'Homologous Series: Add CH2, increase by 14' (Carbon 12 + 2 Hydrogen = 14).

🔢 Key Formulas

$\text{General Formula for Alkanes}: C_{n}H_{2n+2}$

$\text{Delta Mass} = 12(1) + 2(1) = 14 \text{ amu}$

⚙️ Working Principle

Members of a homologous series follow the same general formula. For alkanes, this is $C_{n}H_{2n+2}$ . By increasing the value of $n$ by $1$ unit (e.g., from $n=1$ in $CH_{4}$ to $n=2$ in $C_{2}H_{6}$ ), one carbon atom and two hydrogen atoms are added, resulting in the characteristic $-CH_{2}-$ increment.

📌 Key Points

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Homologous series members share the same functional group and general formula.
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The molecular mass difference between consecutive members is always $14$ u.
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Physical properties like boiling point and melting point show a gradual increase as molecular mass increases.

🛠️ Applications / Uses

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Predicting properties of unknown members of a chemical series.
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Understanding trends in reactivity within hydrocarbon families.

📄 Additional Information

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Atomic mass of Carbon is $12$ u and Hydrogen is $1$ u, so the mass increment is $12 + (2 \times 1) = 14$ u.
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Option D ( $CH_{2}$ ) is correct because every jump from $CH_{4} \rightarrow C_{2}H_{6}$ and $C_{2}H_{6} \rightarrow C_{3}H_{8}$ involves gaining one $C$ and two $H$ atoms.

📊 Diagram / Illustration

✅

D is correct — Successive members of the alkane homologous series differ by a methylene group, represented as $CH_{2}$ .

Core Concepts Used

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Homologous series Hydrocarbons General chemical formulas Molecular mass increments

💡 EXAM TIP

Remember that for any homologous series, the increment is always the same $-CH_{2}-$ unit, whether it is for alcohols ( $-OH$ ), alkenes, or alkanes.

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