Formulae, functional groups and terminology — practice question

Which line shows the relative molecular mass, $M_r$, of the first compound in the specified homologous series?

• Aalkanes, $M_r = 12$
• Balkenes, $M_r = 14$
• Calcohols, $M_r = 32$
• Dcarboxylic acids, $M_r = 60$