Which of the following tests is used to detect the presence of lipids?

Choice A reason: Benedict's test is a test for the presence of reducing sugars, such as glucose or maltose, in a solution. The test involves adding Benedict's reagent, which is a blue solution of copper (II) sulfate, sodium carbonate, and sodium citrate, to the solution and heating it in a water bath. If reducing sugars are present, they reduce the copper (II) ions to copper (I) ions, which form a red, orange, or green precipitate of copper (I) oxide. The color and amount of the precipitate indicate the concentration of reducing sugars in the solution. ¹

Choice B reason: Brown paper test is a test for the presence of lipids, such as fats or oils, in a solution. The test involves placing a drop of the solution on a piece of brown paper and letting it dry. If lipids are present, they leave a translucent spot on the paper, which can be seen by holding the paper against a light source. The test is based on the fact that lipids are nonpolar and do not dissolve in water, but can dissolve in organic solvents and stain the paper. ²

Choice C reason: Biuret test is a test for the presence of proteins or peptides in a solution. The test involves adding Biuret reagent, which is a blue solution of copper (II) sulfate and sodium hydroxide, to the solution. If proteins or peptides are present, they form a complex with the copper (II) ions, which changes the color of the solution to violet or pink. The test is based on the fact that proteins and peptides have peptide bonds, which have nitrogen atoms that can coordinate with the copper (II) ions. ³

Choice D reason: Iodine test is a test for the presence of starch in a solution. The test involves adding iodine solution, which is a brown solution of iodine and potassium iodide, to the solution. If starch is present, it forms a complex with the iodine molecules, which changes the color of the solution to blue-black. The test is based on the fact that starch is a polysaccharide that has a helical structure, which can trap the iodine molecules inside. ⁴

Choice E reason: Wendelspecht test is a fictional test that does not exist in reality. It is a made-up name that has no meaning or relevance to the topic of this question. Therefore, it cannot be a valid answer.

Choice A rationale: Osmotic is incorrect because osmotic is an adjective that describes the movement of water across a semipermeable membrane, not a type of solution. Osmosis is the process by which water moves from a region of high water concentration to a region of low water concentration.

Choice B rationale: Isotonic is incorrect because isotonic is a type of solution that has the same concentration of water as the cell placed in the solution. In an isotonic solution, there is no net movement of water across the cell membrane.

Choice C rationale: Hypertonic is correct because hypertonic is a type of solution that has a lower concentration of water than the cell placed in the solution. In a hypertonic solution, water moves out of the cell and into the solution by osmosis, causing the cell to shrink.

Choice D rationale: Diffusive is incorrect because diffusive is an adjective that describes the movement of molecules from a region of high concentration to a region of low concentration, not a type of solution. Diffusion is the process by which molecules move across a membrane or a space due to their random motion.

Choice E rationale: Hypotonic is incorrect because hypotonic is a type of solution that has a higher concentration of water than the cell placed in the solution. In a hypotonic solution, water moves into the cell and out of the solution by osmosis, causing the cell to swell.