Metabolically the most active of the plasma lipids is: (A) Phospholipids, (B) Cholesterol, (C) Triacylglycerol, (D) Free fatty acids
Answer is D. Free fatty acids 

Plasma lipids consist of triacylglycerols (16%), phospholipids (30%), cholesterol (14%) and cholesteryl esters (36%), and a much smaller fraction of unesterified long chain fatty acids (4%). This latter fraction, the free fatty acids (FAA), is metabolically the most active of the plasma lipids.