A good buffer solution consists of a weak acid with its conjugate base, or a weak base and its conjugate acid. A strong acid or base will never be a good buffer. We will go through each answer choice in detail.

Sulfuric acid is a strong acid and cannot be used in a buffer.

Neither sodium chloride, nor calcium chloride constitute a weak acid or weak base. Both of these are simple salts and will not be able to create a buffer solution.

Hydrochloric acid is a strong acid and cannot be used in a buffer.

In solution, these salts will produce sulfate ions and hydrogen sulfate ions. Hydrogen sulfate is a weak acid and sulfate is its conjugate base. These ions will form a buffer solution.

A buffer system is composed of one of the following scenarios:

1. A weak base with its conjugate acid.

2. A weak acid with its conjugate base.

The only option that does not qualify is the nitrate, nitrite pair. A difference of one oxygen does not make a buffer system.

Compounds with an alcohol group show absorptions in an IR sprectrum from  through . Therefore an absorption of  would correspond to an alcohol. Amide groups show absorptions from  through . Amine groups show absorptions from  through , through ,  through  and  through  (aromatic amines). Carbonyl compounds such as aldehydes show strong absorptions in the IR spectrum at  through .

Distillation is a process of separating a liquid from solutes or other liquids. It utilizes the boiling point differences to separate substances. A substance with a low boiling point will evaporate first in a distillation column and will be isolated first. The question is asking which solution will be isolated first; therefore, we need to figure out which solution has the lowest boiling point. Recall that the boiling point of a solution is elevated when there are more solutes present in the solution. Sodium chloride () contributes two solutes (sodium ions and chloride ions). Calcium nitrate () contributes three solutes (one calcium ion and two nitrate ions). Sucrose does not dissociate into ions in solution; therefore, it only contributes one solute. This means that the sucrose solution will have the lowest amount of molecules in solution, the lowest boiling point, and will be separated first.

There are two types of distillation. Simple distillation is used to separate molecules that have very different boiling points. Fractional distillation is used to separate molecules with small differences in boiling points. Fractional distillation is often used if the difference between boiling points is less than . In simple distillation, the vapor is immediately collected in a condenser. On the other hand, fractional distillation allows vapor to condense and revaporize several times. These repeated cycles allow fractional distillation to purify the vapor better than simple distillation.

Distillation is used to separate molecules with different boiling points. Simple distillation is used to separate molecules with vastly different boiling points. Fractional distillation, on the other hand, is a refined form of simple distillation that can be used to separate molecules with similar boiling points. Note that fractional distillation can separate molecules with either different or similar boiling points; therefore, fractional distillation can be used to separate any of the given mixtures. 

Rate of distillation is increased when the ability of a substance to become a vapor is increased. Recall that vapor is created when enough heat is applied to the liquid. The temperature at which the liquid becomes vapor is called the boiling point. A liquid turns into a vapor when the vapor pressure (pressure applied by the vapor from the liquid) equals the atmospheric pressure. Decreasing the atmospheric pressure will make it easier for the liquid to turn into a vapor; therefore, this will increase the rate of distillation.

Decreasing the vapor pressure will remove vapor from system. This will make it harder to distill substances. Decreasing temperature will move the system away from the boiling point, thereby decreasing the amount of vapor. Decreasing mole fraction of the substance will decrease the surface area of the substance (at the surface of the solution). Liquid molecules need to be present at the surface to escape the solution and become vapor; therefore, decreasing mole fraction will decrease the amount of vapor.

TLC is a laboratory technique commonly used to separate components of a mixture. Mixtures are placed on the TLC plate (stationary phase), which is then transferred to a jar containing the solvent. The solvent travels through the plate and carries components of the mixture along with it. Based on its properties, each component is dragged to different distances on the plate. The relative distances travelled by each component can be used for separation and identification.

It is important to place a lid on the jar because the solvent will be a volatile substance. An open system will allow for the solvent to evaporate from the TLC plate and reduce the amount of solvent travelling through the plate. The solvent in the solution will evaporate, but it is negligible and inconsequential to the data collected on the TLC plate. 

Thin layer chromatography (TLC) is used to separate components in a mixture. Components are separated on a TLC plate because each component travels a different distance. The distance travelled depends on several factors. One of those factors is polarity; therefore, TLC can used to determine polarity of substances.

TLC is not useful for identifying substances. Other techniques such as NMR and IR spectroscopy are useful for identifying individual components. The R_f value of a compound can help identify it in a broad sense, but this technique provides only very rudimentary identification capabilities.

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).