Gas chromatography and thin layer chromatography differ by the phases of both the mobile and stationary phases. In gas chromatography, the mobile phase is a gas and the stationary phase is a liquid. In thin layer chromatography, the mobile phase is a liquid and the stationary phase is a solid.

In the normal phase chromatography system described, the most nonpolar compound would elute first and the most polar compound would elute last. The silica stationary phase will interact with more polar molecules, while the hexane mobile phase will carry nonpolar molecules. This would slow the progress of polar molecules as they bond to the silica, and enhance the progress of nonpolar molecules as they interact with the mobile phase.

Compound C is the most nonpolar compound because it contains only hydrogen and carbon. Compounds A and B are more polar because of the presence of oxygen, and hence the presence of polarized carbon-oxygen bonds. The alcohol group of compound B makes this compound the most polar of the three molecules by virtue of hydrogen bonding capabilities as well as the carbon-oxygen dipole. Compound B would thus elute last.

The R_f factor is a ratio of the compound's travel distance compared to the solvent's travel distance; this value will always be between 0 and 1. As a result, a nonpolar compound would not be able to travel twice the distance or have twice the R_f factor as the mystery compound. This would result in a value of 1.2.

The only thing we can predict confidently is that a more polar compound would travel a shorter distance than the mystery compound, which result in a lower R_f factor. 

The Hofmann product is the most favored product in a Hofmann elimination reaction. The reaction follows an E2 mechanism, where a quaternary ammonium salt is able to be removed from a hydrocarbon, resulting in an alkene product. This reaction results in the least substituted alkene being the primary product.

The Wittig reaction is used to make an alkene from a ketone or aldehyde. The ylide (RPPh₃) attaches to the substrate via nucleophilic addition, with the negative carbanion attaching to the ketone or aldehyde. The phosphorus atom carries a positive charge, balancing the carbanion.

All other listed answer choices are true. The products of the reaction are an alkene (cis and trans) with the addition of the R group of the ylide and Ph₃PO.

The Wittig reaction involves the reaction of a phosphonium ylide (generated by treating a phosphonium salt with a strong base) with a ketone or aldehyde.

The reaction proceeds through a phosphaoxetane (4-membered ring containing both phosphorus and oxygen) intermediate to generate a new compound containing a carbon-carbon double bond, plus a phosphine oxide byproduct. It does not form trans double bonds exclusively; sometimes, a mixture of cis and trans isomers are obtained, and sometimes the cis isomer is the predominant product. 

The Wittig reaction involves a ketone or aldehyde reacting with a phosphorus ylide, a molecule with a negatively charged carbanion. The ketone will undergo nucleophilic addition and form a betaine. This intermediate will then form an alkene with a triphenylphosphine oxide being released. The Wittig reaction will form a mixture of both cis and trans isomers if the carbanion has two different substituents.

Wittig general reaction:

A hemiketal compound is the result of nucleophilic attack by an alcohol (1-propanol) on the carbonyl of a ketone (acetone). The previously double-bonded oxygen now bears a negative charge, and deprotonates the now positively charged attacking alcohol. The hemiketal of acetone will have a hydroxy group and an -OCH₃ group bound to the central carbon.

This reaction shows nucleophilic acyl attack on a carbonyl group by the ammonia molecule. This reaction leads to the loss of oxygen as water, and eventually the formation of an imine. Note the difference between each product type. An imine is a nitrogen with one nitrogen-carbon double bond and one substituent. An enamine is formed from a nitrogen with no double bonds. An amide is a nitrogen bound to a carbonyl carbon.

The correct answer is hemiacetal and acetal. The partial positive character of a carbonyl carbon makes it susceptible to nucleophilic attack. An alcohol's oxygen has free electrons, and therefore can serve as a nucleophile. As the bond between the attacking alcohol's oxygen and the carbonyl carbon forms, the pi bond of the carbonyl group is lost. Once the attacking alcohol's oxygen is deprotonated, the resulting product is an ether (from the attacking alcohol) and a new hydroxyl group (from the now protonated carbonyl oxygen). The resulting molecule is referred to as the hemiacetal product.

Subsequent addition of alcohol leads to the loss of the hydoxyl group as water, resulting in the second ether chain to the original carbon, which is referred to as the acetal product.

The same reaction takes place with ketones as well. With ketones, the first addition of alcohol results in the hemiketal product, and the second addition of alcohol results in the ketal product.

It is important to remember the following material for analyzing acetal and ketal reactions.

1. These alcohol addition reactions only occur with aldehydes and ketones.

2. Hemiacetal and hemiketal products can be identified by having one ether chain and one hydroxyl group attached to the original carbonyl carbon. Acetal and ketal groups have two ether groups attached to the original carbonyl carbon.

3. Acetal and hemiacetal groups will have a hydrogen attached to the original carbonyl carbon, where ketal and hemiketal groups will have carbon chains attached to the original carbonyl carbon (with no bound hydrogens).