The answer would be C8H18, or octane. Column chromatography is a separation technique that works off of polarity. The stationary phase, in column chromatography, are non-modified silica gels. Silica gels are normally polar. This means the solvent that will elute first are non-polar molecules...then polar molecules. The polar silica gels have a stronger interaction with polar molecules like CH3OH, and therefore will lag the solvent. Additionally, as you decrease the carbons, in hydrocarbons, the molecule becomes more polar. This is not C6H6 isn't the answer and octane is.
