Which one of the following is not a fossil fuel?

50 The molecular formula of an organic compound is C₄₈H_94. This compound belongs to the homologous Series of: 51 One of the following molecular formulae represent a ketone. This formula is: 53 Butanone is a four-carbon compound having the functional group: 54 The molecular formula of the third member of the homologous series of ketones is: