Which of the following pair of compound - general formula is correct?

I. Alkenes - $C_nH − 2n$

II. Alkanes - $C_nH − 2n − 1$

Only I

The correct answer is option 2. Only I.

Let's break down the explanation for each compound and its general formula:

I. Alkenes - \(C_nH_{2n}\):
Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (\(C=C\)). The general formula for alkenes is \(C_nH_{2n}\), where \(n\) represents the number of carbon atoms in the molecule.

For example, if \(n = 2\), the formula becomes \(C₂H₄\), representing ethene.

II. Alkanes - \(C_nH_{2n + 1}\):
Alkanes are hydrocarbons that contain only single bonds between carbon atoms. The general formula for alkanes is \(C_nH_{2n + 1}\), where \(n\) represents the number of carbon atoms in the molecule.

For example, if \(n = 2\), the formula becomes \(C₂H₆\), representing ethane.

So, based on the correct general formulas for alkenes and alkanes:

Alkenes have the general formula \(C_nH_{2n}\) (Option I is correct).
- Alkanes have the general formula \(C_nH_{2n + 1}\) (Option II is incorrect).

Therefore, the correct answer is option 2. Only I.