To solve this problem we need to recall the definition of R_f.

The solvent is typically the most mobile substance on a TLC plate; therefore, it travels the farthest distance. This means that R_f is always less than one because the numerator of R_f is always smaller than the denominator. The question states that the R_f value is 2. Since this is greater than 1, the results don’t seem valid. This value indicates that the solute compounds were able to teravel farther on the TLC plate than the solvent (mobile phase).

Compounds A and B are in the same mixture; therefore, they will be separated using the same TLC plate. Recall the definition of R_f.

Since the same TLC plate was used, the denominator for both compound A and B will be the same (the total distance travelled by solvent alone is the same for a TLC plate). To separate them effectively, compounds must have travelled different distances along the plate. The best separation occurs when the difference between the distances travelled by the compounds is greatest.

Let’s assume the denominator to be 1 for both compounds. This means that the numerator is equal to the R_f value. If we compare the given R_f values with each other we realize that R_f values of 0.4 and 0.2 will give the biggest difference between the distances travelled by compounds A and B (difference is ); therefore, this will have the best separation. 

Gel electrophoresis is a technique used to separate molecules based on size or charge. Charged particles can be separated because they migrate towards different ends of the gel.

Negatively charged particles always migrate towards the positive pole whereas positively charged particles always migrate towards the negative pole (opposites attract). In gel electrophoresis, the positive pole is called the anode and the negative pole is called the cathode; therefore, the charged particles will migrate to the respective nodes.

The isoelectric point is the pH at which a charged particle loses its charge and becomes neutral; therefore, the pI is only a property of the species (not its environment). When the pH of the environment equals the pI of the molecule, the electrical charge on the molecule disappears. A basic environment is characterized by a high pH. If the pH of the environment is higher than the pI, then the environment is basic. The size of the species is usually represented by mass or weight, not by pI.

pI of a substance affects other chemical properties, such as solubility. Charged species are polar and are likely to dissolve in polar solvents whereas uncharged species (when pH = pI) are likely nonpolar and are more soluble in nonpolar solvents.

A pH gradient in a gel facilitates the separation of charged species. The proteins in the mixture encounter different pHs as they travel through the gel. The driving force for the proteins is the electric force. Recall that each protein has an isoelectric point; when the protein's environmental pH equals the isoelectric point, the protein will become neutral and stop migrating (it loses the electric force). The physiological pH is about 7.4. Several amino acids are uncharged at this pH; however, these amino acids will become charged when presented in a different pH environment; therefore, these proteins will be charged and be able to migrate through the gel because of the pH gradient.

The protein will stop migrating when the pH of the environment (gel) equals the pI of the protein. Different types of gel electrophoresis are used to separate molecules based on charge and size. A pH gradient is used to separate molecules based on charge, whereas SDS-PAGE is used to separate molecules based on size. All types of macromolecules (nucleic acids, proteins, lipids, and carbohydrates) can be separated using gel electrophoresis.

SDS is a substance added to polyacrylamide gels to separate substances based on size. This method is called SDS-PAGE. SDS binds to the secondary structure of proteins and gives them an overall negative charge; the bigger the substance the bigger the negative charge. The larger mass compensates for the bigger charge; therefore, SDS makes it so that the mass-to-charge ratio of all substances is the same. This standardizes the electric force experienced by each molecule, making size the only driving force for migration through the gel.

Since heat can be considered a reactant (endothermic), if heat is decreased, ADP is increased according to Le Chatelier’s Principle. If a reactant is removed, the equilibrium will shift toward the reactants. In this reaction, ADP and heat are both reactants.

This question ties together the reaction for oxidation of glucose with several thermodynamic principles.

The first option, stating that there is an increase of entropy, is true. When balanced, we see that there is an increase in total number of molecules when the reaction completes; thus, there will be an increase in entropy.

The second option states that enthalpy, or , is less than than zero. This is also true, as it implies that this is an exothermic (or heat generating) reaction. The oxidation of glucose is how our bodies generate heat and keep homeostasis.

The third option, stating that Gibb's free energy is zero at equilibrium, is also true. Any equation will have  at equilibrium.

The last option, stating that oxygen is the reducing agent, is false. Oxygen is actually the oxidizing agent and is itself reduced.

Since glycolysis is an exothermic reaction (ΔH is negative), enthalpy does not increase. As for entropy, the reaction begins with a large molecule and ends with smaller molecules, therefore entropy increases.

ΔG and ΔH are both negative for glycolysis, meaning that the reaction is exergonic and exothermic.