Question

Which of the following is an alkene?

• A. C\(_2\)H\(_6\)
• B. C\(_2\)H\(_4\)
• C. C\(_3\)H\(_8\)
• D. C\(_4\)H\(_{10}\)

Hint:

Key Fact: Alkenes: \( C_nH_{2n} \); look for a double bond in the structure.

Answer 1

The Correct Option is B

To determine which compound is an alkene, we need to understand the characteristics of alkanes, alkenes, and alkynes:

• Alkanes: Saturated hydrocarbons with single bonds only, following the general formula C_nH_2n+2.
• Alkenes: Unsaturated hydrocarbons containing at least one carbon-carbon double bond, following the general formula C_nH_2n.
• Alkynes: Unsaturated hydrocarbons with at least one carbon-carbon triple bond, following the general formula C_nH_2n-2.

Given the options:

• C₂H₆: This follows the alkane formula (C₂H₂₍₂₎₊₂) = C₂H₆. Therefore, it is an alkane.
• C₂H₄: This fits the alkene formula (C₂H₂₍₂₎) = C₂H₄. Thus, it is an alkene.
• C₃H₈: This matches the alkane formula (C₃H₂₍₃₎₊₂) = C₃H₈. Hence, it is an alkane.
• C₄H₁₀: This conforms to the alkane formula (C₄H₂₍₄₎₊₂) = C₄H₁₀. Therefore, it is an alkane.

From the options given, C₂H₄ is the only compound that satisfies the formula of an alkene, as it contains the double bond necessary for an unsaturated hydrocarbon.

Answer 2

Alkenes are hydrocarbons with at least one double bond and follow the general formula \( C_nH_{2n} \)

C\(_2\)H\(_4\): Ethene — it has a double bond → alkene

C\(_2\)H\(_6\): Ethane — single bonds only → alkane

C\(_3\)H\(_8\): Propane → alkane

C\(_4\)H\(_{10}\): Butane → alkane