1 markMCQSection A

Which one of the following hydrocarbons is different from the others?

Carbon and its Compounds

Chains, Branches and Rings

Options

(A)

C_4H_{10}

(B)

C_7H_{14}

(C)

C_5H_{12}

(D)

C_2H_6

Official Answer

The hydrocarbon $C_7H_{14}$ is different from the others because it is an unsaturated hydrocarbon (alkene), whereas the other three ( $C_4H_{10}$ , $C_5H_{12}$ , and $C_2H_6$ ) are saturated hydrocarbons (alkanes).

AlkaneAlkeneSaturatedUnsaturated

C_nH_{2n+2}

C_nH_{2n}

Marking Scheme

11 Mark for identifying Option B as the correct answer with the justification of saturated vs. unsaturated hydrocarbons.

Hint

Apply the general formula for alkanes ( $C_nH_{2n+2}$ ) and alkenes ( $C_nH_{2n}$ ) to classify each hydrocarbon.

Quick Oral Answer

$C_7H_{14}$ is an alkene (unsaturated), while $C_2H_6$ , $C_4H_{10}$ , and $C_5H_{12}$ are alkanes (saturated). Alkanes follow the formula $C_nH_{2n+2}$ , whereas alkenes follow $C_nH_{2n}$ .

Analysis & Explanation

To identify the odd hydrocarbon, we analyze their molecular formulas using the general formulas of homologous series:

Alkanes (Saturated Hydrocarbons): General formula is $C_nH_{2n+2}$ .

For $n = 2$ : $C_2H_{2(2)+2} = C_2H_6$ (Ethane) -> Alkane
For $n = 4$ : $C_4H_{2(4)+2} = C_4H_{10}$ (Butane) -> Alkane
For $n = 5$ : $C_5H_{2(5)+2} = C_5H_{12}$ (Pentane) -> Alkane

Alkenes (Unsaturated Hydrocarbons): General formula is $C_nH_{2n}$ .

For $n = 7$ : $C_7H_{2(7)} = C_7H_{14}$ (Heptene) -> Alkene

Since $C_7H_{14}$ is an alkene containing a double bond, it is unsaturated and chemically more reactive than the other three saturated alkanes. Thus, Option B is the correct choice.

Common Mistakes

1Students often fail to recognize the general formula and try to guess based on the number of carbon atoms alone.
2Confusing the general formula of alkenes ( $C_nH_{2n}$ ) with alkynes ( $C_nH_{2n-2}$ ).

Interesting Facts

Alkanes are also known as 'paraffins' (meaning little affinity) because they are relatively unreactive, whereas alkenes are called 'olefins' because they form oily liquids on reaction with chlorine.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2024?

This question carries 1 mark in the CBSE Class 10 Science 2024 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Carbon and its Compounds" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Chains, Branches and Rings" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2024 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2024 paper.