Which molecular formula represents an alkane?

The molecular formula that correctly represents an alkane is CnH2n+2. Alkanes are saturated hydrocarbons, meaning they contain only single bonds between carbon atoms and are fully "saturated" with hydrogen atoms.

In the formula CnH2n+2, 'n' represents the number of carbon atoms in the alkane. For every carbon atom, there are two hydrogen atoms plus an additional two hydrogen atoms, resulting in a total of 2n + 2 hydrogen atoms. This formula is characteristic of alkanes, such as methane (CH4) and ethane (C2H6), highlighting that they possess the maximum number of hydrogen atoms that can bond to the carbons, maintaining the saturated state.

The other formulas do not define alkanes: CnH2n suggests a structure that is unsaturated, meaning it could include alkenes or cycloalkanes. CnH2n-2 implies a reduction in hydrogen atoms which would also not represent a saturated compound, and CnHn does not account for the additional hydrogen atoms needed in alkanes, indicating it is not a valid formula for this category of hydrocarbons.