An organic compound 'A' with molecular formula CH₄O reacts with HI to give an alkyl iodide which than reacts with potassium cyanide to produce 'B'. Compound 'B' on reduction followed by reaction with HNO₂ gives an alcohol which on oxidation gives 'C'. Compound 'C' on oxidation followed by reaction with CH₃MgBr gives 'D' which on hydrolysis gives compound 'E' which is also an alcohol. 

Which of the following is known as Grignard reagent?

CH₃MgBr

The correct answer is option 1. \(CH_3MgBr\)

Let us delve into what makes a Grignard reagent and why \( \text{CH}_3\text{MgBr} \) fits this description:

Grignard reagents are organomagnesium compounds of the general formula \( \text{R-Mg-X} \), where \( \text{R} \) is an alkyl or aryl group and \( \text{X} \) is a halogen atom (typically bromine or chlorine). These compounds were discovered by the French chemist François Auguste Victor Grignard, which is why they are named after him.

Characteristics of Grignard Reagents:

Structure:

The carbon atom bonded to magnesium in a Grignard reagent is nucleophilic and highly reactive due to the polar nature of the magnesium-carbon bond. The magnesium atom carries a partial positive charge, making the carbon atom electron-rich and reactive towards electrophiles.

Preparation:

Grignard reagents are typically prepared by reacting alkyl or aryl halides (such as alkyl bromides or alkyl chlorides) with magnesium metal in anhydrous ether or tetrahydrofuran (THF) as a solvent. For example, \( \text{CH}_3\text{Br} \) reacts with magnesium metal to form \( \text{CH}_3\text{MgBr} \).

Reactivity:

Grignard reagents are used as strong bases and nucleophiles in organic synthesis. They react readily with a variety of electrophiles, including carbonyl compounds (such as aldehydes, ketones, esters), alkyl halides, epoxides, and others, forming carbon-carbon bonds and other functional group transformations.

Explanation of Options:

1. \(CH_3MgBr\): This is methyl magnesium bromide, \( \text{CH}_3\text{MgBr} \), which is a classic example of a Grignard reagent. It is formed by reacting methyl bromide (\( \text{CH}_3\text{Br} \)) with magnesium metal.
 

2. \(CH_3CH_2NH_2\): This is ethylamine, \( \text{CH}_3\text{CH}_2\text{NH}_2 \), which is not a Grignard reagent. It is an amine compound and does not contain a magnesium atom bonded to a carbon atom.

3. \((CH_3)_2CH-OMgBr\): This seems to represent a hypothetical structure involving isopropylmagnesium bromide (\( (\text{CH}_3)_2\text{CH}-\text{OMgBr} \)), which is not typically recognized as a Grignard reagent. Grignard reagents usually have a halogen directly bonded to magnesium, not an alkoxide group.

Conclusion: Among the options provided, \( \text{CH}_3\text{MgBr} \) is the compound known as a Grignard reagent. It exemplifies the characteristics of Grignard reagents: organomagnesium compounds used as strong bases and nucleophiles in organic synthesis.