How do you identify the number of carbon atoms in a linear alkane?

The correct choice for identifying the number of carbon atoms in a linear alkane is to examine the molecular formula. The general formula for linear alkanes is C_nH_(2n+2), where n represents the number of carbon atoms. By analyzing this formula, you can directly determine the number of carbon atoms present: for instance, if the formula is C_5H_{12}, it clearly indicates that there are five carbon atoms.

This method is straightforward and effective because the molecular formula encapsulates both the type of atoms (carbons and hydrogens) and their quantities. The other approaches listed, such as analyzing molecular weight or boiling point, do not provide direct information on the number of carbon atoms in a linear alkane. Functional groups are also unrelated to the counting of carbon atoms in alkanes since alkanes are straightforward hydrocarbons without functional groups. Hence, focusing on the molecular formula is the most accurate way to determine the carbon count in linear alkanes.