Assertion: Hydroxyketones are not directly used in Grignard reaction.
Reason: Grignard reagents react with the hydroxyl group.

The correct answer is option 'A' which states that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

Explanation:

Grignard Reaction:
The Grignard reaction is a useful synthetic tool in organic chemistry that involves the formation of a carbon-carbon bond. It was discovered by French chemist Victor Grignard and it involves the reaction of an organic halide with magnesium metal in anhydrous ether to form a Grignard reagent. These Grignard reagents are highly reactive and can be used to synthesize a wide range of organic compounds.

Hydroxyketones:
Hydroxyketones are organic compounds that contain both a hydroxyl group (-OH) and a ketone group (C=O) within the same molecule. They are also commonly referred to as ketol compounds. Some examples of hydroxyketones include acetone (CH3C(O)CH3) and 2-butanone (CH3C(O)CH2CH3).

Assertion and Reason:
The assertion states that hydroxyketones are not directly used in Grignard reactions. This is because the presence of a hydroxyl group in hydroxyketones can lead to unwanted side reactions with Grignard reagents. The hydroxyl group can react with the Grignard reagent to form an alkoxide, rather than the desired carbon-carbon bond formation.

The reason given for this assertion is that Grignard reagents react with the hydroxyl group. This is true because Grignard reagents are highly nucleophilic and can react with various electrophilic functional groups, including the hydroxyl group. These reactions typically result in the formation of alkoxides.

Explanation of the Reason:
Grignard reagents are strong bases and nucleophiles, and they have the ability to attack electrophilic carbon atoms. In the presence of a hydroxyl group, the Grignard reagent can attack the carbonyl carbon of the hydroxyketone, leading to the formation of an alkoxide. This reaction competes with the desired carbon-carbon bond formation and can reduce the overall yield of the desired product.

To avoid this unwanted side reaction, hydroxyketones are often converted into their corresponding acetals or ketals before being used in Grignard reactions. These protecting groups can temporarily mask the hydroxyl group, preventing its reaction with the Grignard reagent. After the Grignard reaction is complete, the protecting group can be removed to reveal the hydroxyl group.

Conclusion:
In conclusion, hydroxyketones are not directly used in Grignard reactions due to the reactivity of the hydroxyl group with Grignard reagents. The hydroxyl group can undergo a side reaction to form an alkoxide, reducing the yield of the desired product. Protecting groups, such as acetals or ketals, are often employed to temporarily mask the hydroxyl group and prevent this unwanted reaction.