1 markVery Short AnswerSection A

Write the name and formula of the 2nd member of homologous series having general formula $C_nH_{2n}$ .

Carbon and its Compounds

Homologous Series

Official Answer

The general formula $C_nH_{2n}$ represents the homologous series of alkenes (unsaturated hydrocarbons with one double bond). The first member of this series is ethene ( $C_2H_4$ ) where $n=2$ . Therefore, the second member is propene, which has the molecular formula $C_3H_6$ .

Propene

C_3H_6

Alkenes

Marking Scheme

1Name: Propene (0.5 mark)
2Formula: $C_3H_6$ (0.5 mark)

Hint

Recall that the alkene series starts with two carbon atoms because a double bond cannot exist with only one carbon atom.

Quick Oral Answer

The second member of the $C_nH_{2n}$ series is propene ( $C_3H_6$ ). It belongs to the alkene family, characterized by at least one carbon-carbon double bond.

Analysis & Explanation

The general formula for alkenes is $C_nH_{2n}$ . Since a double bond requires at least two carbon atoms, the series starts with $n=2$ .

1st member ( $n=2$ ): Ethene ( $C_2H_4$ )
2nd member ( $n=3$ ): Propene ( $C_3H_6$ )
3rd member ( $n=4$ ): Butene ( $C_4H_8$ )

Common Mistakes

1Writing 'methene' as the first member (it does not exist).
2Confusing the formula with alkanes ( $C_nH_{2n+2}$ ) or alkynes ( $C_nH_{2n-2}$ ).

Interesting Facts

Propene is the second simplest alkene and is a byproduct of oil refining and natural gas processing.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2015?

This question carries 1 mark in the CBSE Class 10 Science 2015 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 "Homologous Series" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2015 paper?

This is a Very Short Answer question from Section A in the CBSE Class 10 Science 2015 paper.