A diverse group of organic substances that are insoluble in water; includes triglycerides, phospholipids, and sterols.

• A. Carbohydrates
• B. Proteins
• C. Lipids
• D. Nucleic acids

Answer: (C)

Nonpolar, water-repelling nature defines this group of organic substances. Lipids are diverse and include triglycerides, phospholipids, and sterols. Triglycerides consist of glycerol with three fatty acids, whose long hydrocarbon chains dominate the molecule and drive water-insolubility. Phospholipids have a dual character: two hydrophobic fatty acid tails and a hydrophilic phosphate-containing head; in water they don’t dissolve but arrange into membranes or micelles because of this amphipathic structure. Sterols like cholesterol feature fused ring systems that are largely nonpolar with only a small polar region, making them insoluble in water as well. By contrast, carbohydrates, proteins, and nucleic acids are typically soluble in water due to numerous polar groups and charges that interact favorably with water. The description points to lipids, a broad category characterized by their hydrophobic behavior and inclusion of triglycerides, phospholipids, and sterols.