Here's why:

* Alkanes are hydrocarbons (molecules containing only carbon and hydrogen) with single bonds between all carbon atoms.

* Alkenes contain at least one carbon-carbon double bond.

* Alcohols contain a hydroxyl (-OH) group.

The name "3-methyloctane" tells us:

* Octane indicates an eight-carbon chain.

* 3-methyl indicates a methyl group (CH3) attached to the third carbon in the chain.

Since there's no mention of double bonds or hydroxyl groups, it's an alkane.