In unsaturated lipid molecules, carbon-carbon double bonds are found

Explanation

The correct answer is 'within fatty acids only.' In unsaturated lipid molecules, carbon-carbon double bonds are present within the fatty acid chains. These double bonds introduce kinks in the chain, affecting the lipid's fluidity and melting point. Glycerol, on the other hand, is a simple three-carbon molecule that serves as the backbone for triglycerides and phospholipids, and does not contain carbon-carbon double bonds. Option A is incorrect because glycerol does not have these double bonds. Option C is incorrect because the connection between glycerol and fatty acids involves ester bonds, not carbon-carbon double bonds. Option D is incorrect because while the fatty acids contain double bonds, glycerol does not.