When alkyl cynide react with grignard reagent ketone is obtained
it is method of preparation of the ketone

Grignard reagents are organometallic compounds that contain a carbon-metal bond, where the metal is typically magnesium (Mg). They are highly reactive and are commonly used for the synthesis of alcohols, carboxylic acids, and ketones.

To understand which of the given compounds will give a ketone with a Grignard reagent, we need to consider the reaction mechanism involved.

**Reaction Mechanism:**
When a Grignard reagent reacts with a carbonyl compound, such as an aldehyde or ketone, a nucleophilic addition reaction takes place. The carbon atom of the carbonyl group is attacked by the nucleophilic carbon atom of the Grignard reagent, resulting in the formation of an alkoxide intermediate.

This alkoxide intermediate can undergo further reaction to yield different products depending on the conditions. If the reaction is carried out in the presence of water or an acid, the alkoxide intermediate will be protonated, resulting in the formation of an alcohol. However, if the reaction is carried out in the absence of water or an acid, the alkoxide intermediate will undergo a rearrangement to form a ketone.

**Analysis of Given Compounds:**
a) Formaldehyde: Formaldehyde is an aldehyde, and when it reacts with a Grignard reagent, it will initially form an alkoxide intermediate. However, under the reaction conditions, this alkoxide intermediate will be protonated by water or acid, resulting in the formation of an alcohol rather than a ketone.

b) Ethyl alcohol: Ethyl alcohol is not a carbonyl compound and therefore cannot directly react with a Grignard reagent to form a ketone.

c) Methyl cyanide: Methyl cyanide is a nitrile compound and also not a carbonyl compound. It cannot directly react with a Grignard reagent to form a ketone.

d) Methyl iodide: Methyl iodide is an alkyl halide and does not contain a carbonyl group. It cannot directly react with a Grignard reagent to form a ketone.

Therefore, the correct answer is option 'C' - Methyl cyanide. None of the other given compounds are capable of giving a ketone when reacted with a Grignard reagent.