Which objective lens requires oil to be applied?
Multiple choice.

Choice A rationale: Density of media affects the rate of diffusion because it influences the frequency of collisions between the diffusing molecules and the molecules of the medium. The denser the medium, the slower the diffusion rate, and vice versa.

Choice B rationale: Size of molecules affects the rate of diffusion because it determines how easily the molecules can move through the spaces between the molecules of the medium. The smaller the molecules, the faster the diffusion rate, and vice versa.

Choice C rationale: Concentration gradient affects the rate of diffusion because it is the difference in concentration of the diffusing molecules between two regions. The higher the concentration gradient, the faster the diffusion rate, and vice versa.

Choice D rationale: Membrane permeability affects the rate of diffusion because it is the ability of the membrane to allow the diffusing molecules to pass through it. The more permeable the membrane, the faster the diffusion rate, and vice versa.

Choice E rationale: pH affects the rate of diffusion because it is the measure of acidity or alkalinity of the medium. pH can affect the charge and shape of the diffusing molecules, which can affect their ability to cross the membrane or interact with the molecules of the medium. pH can also affect the membrane permeability by altering the charge and shape of the membrane proteins.

Choice A rationale: Iodine is a chemical element that forms a brown solution of iodine and potassium iodide, known as iodine solution. When this solution is added to a sample that contains starch, it forms a complex with the starch molecules, which changes the color of the solution to blue-black. This is based on the fact that starch is a polysaccharide that has a helical structure, which can trap the iodine molecules inside. ²

Choice B rationale: Biuret is a chemical compound that forms a blue solution of copper (II) sulfate and sodium hydroxide, known as biuret reagent. When this reagent is added to a sample that contains proteins or peptides, it forms a complex with the copper (II) ions, which changes the color of the solution to violet or pink. This 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 C rationale: Benedict's is a chemical compound that forms a blue solution of copper (II) sulfate, sodium carbonate, and sodium citrate, known as Benedict's reagent. When this reagent is heated with a sample that contains reducing sugars, such as glucose or maltose, it reduces the copper (II) ions to copper (I) ions, which form a red, orange, or green precipitate of copper (I) oxide. This is based on the fact that reducing sugars have free aldehyde or ketone groups that can donate electrons to the copper (II) ions. ⁴

Choice D rationale: Phenol red is a chemical compound that forms a red solution that is used as a pH indicator. When this solution is added to a sample that has an acidic or neutral pH, it remains red or turns yellow. When this solution is added to a sample that has an alkaline pH, it turns pink or fuchsia. This is based on the fact that phenol red has a sulfonated hydroxyquinone group that can lose or gain protons depending on the pH of the solution. ⁵

Choice E rationale: Sudan IV is a chemical compound that forms a red powder that is used as a stain for lipids. When this powder is dissolved in a solvent and added to a sample that contains lipids, such as fats or oils, it dissolves in the lipids and stains them red. When this solution is added to a sample that does not contain lipids, it remains in the solvent and does not stain the sample. This is based on the fact that Sudan IV is a nonpolar compound that can dissolve in nonpolar substances like lipids, but not in polar substances like water. ⁶.