In order to drive the reactant, we must first convert the alcohol group on the ethanol into a carboxylic acid. We do so by using the oxidizing agent, , a very strong oxidizing agent that is well known to oxidize primary alcohols into carboxylic acids (among other functions). Once we have our carboxylic acid, we can simply use  to convert our carboxylic acid into an acid halide to attain our desired final product.

 is a strong oxidizing agent.

Not only can  reduce secondary alcohols into ketones, but it can reduce primary alcohols and aldehydes into carboxylic acids.

The reaction given would give a ketone. This type of reaction is called an oxidation reaction. Oxidation of a secondary alcohol as in the reaction given by  (sodium dichromate) in an aqueous solution of  (acetic acid) solvent yields a ketone. However, if we performed the same reaction with a primary alcohol, a carboxylic acid would have formed.

The Jones reagent can convert primary alcohol to acids and secondary alcohols to ketones. The Tollen's test only converts aldehydes to carboxylic acids. PCC can only convert primary and secondary alcohol to aldehydes and ketones, respectively.  and  are reducing agents. 

To form the aldehyde, the alcohol must be oxidized. However, potassium permanganate and chromic acid are too strong and would yield a carboxylic acid. Ozonolysis works with alkenes and oxygen over platinum would not react. PCC is correct because it will oxidize the alcohol to form an aldehyde but is too weak to continue on to form the carboxylic acid.

Sodium borohydride donates a hydride ion to a ketone or aldehyde. In order to form a ketone or aldehyde, a nucleophile must attack the carbonyl group. This is because the ketone or aldehyde has an electrophilic carbon—a nucleophile must attack it in order for any reaction to occur. A hydride ion is the only answer choice that plays the role of a nucleophile.

The correct choice, CeCl₃ and NaBH₄ in MeOH, shows reagents know as "Luche conditions," which are able to modify the reactivity of sodium borohydride to reduce the carbonyl to an alcohol without affecting alkene groups. This occurs as the cerium ion coordinates strongly to the carbonyl oxygen, which subsequently greatly enhances the electrophilicity at the carbonyl carbon. Nucleophilic attack of the hydride readily occurs, simultaneously destroying the electropilicty of the beta carbon of the alkene, such that it will not be reduced by the hydride reagent.

The incorrect answer choices would give various undesired products as detailed below:

NaBH₄ in MeOH

Use of unmodified sodium borohydride would result in a 1,4 conjugate addition reaction, saturating the alkene, with a subsequent reduction of the ketone to an alcohol.

LiAlH₄ in THF

Use of lithium aluminum hydride would give the same product as use of unmodified sodium borohydride, following the same reduction mechanism.

Pd and H₂ in hexanes

This reagent will give reduction of the alkene only.

Pd, BaSO₄, and H₂ in hexanes

This reagent combination, known as Lindlar's catalyst, will also reduce the alkene only. This reagent is typically used to selectively reduce an alkyne to an alkene.

Sodium borohydride is a reducing agent with formula . It is a reducing agent, but it is not extremely strong. It reduces ketones to alcohols, but it does not affect carboxylic acids. 3-pentanone is the only ketone of the given choices. It would be reduced to 3-pentanol.

These are all true uses of .

The reaction between magnesium and an alkyl halide in anhydrous ether results in a Grignard reagent.

An organolithium would result from the same process, but the magnesium would need to be replaced by two equivalents of lithium. Alcohols are products of reactions between a Grignard reagent and a carbonyl.