Here's why:

* Alkanes are hydrocarbons (compounds made of only carbon and hydrogen) with single bonds between all the carbon atoms.

* The general formula for alkanes is CnH2n+2.

* In C3H8, we have 3 carbon atoms (C3) and 8 hydrogen atoms (H8), which perfectly fits the alkane formula (3 x 2 + 2 = 8).

Therefore, C3H8 is classified as an alkane.