Lipids store roughly twice as much energy per gram as carbohydrates. Which property of lipid molecules best explains this?

Lipid fatty-acid tails are long chains of carbon–hydrogen bonds. Oxidizing each C–H bond releases energy, so the more C–H bonds per gram, the more energy is stored. Carbohydrates have fewer C–H bonds per carbon because oxygen atoms are already attached. Water insolubility relates to *where* lipids are stored, not how much energy they hold. Lipids are not true polymers. Lipids contain almost no nitrogen — that is a feature of proteins and nucleic acids.