Which statement is true about Grignard reagents?

• A. They are stable in water
• B. They must be prepared under strictly anhydrous conditions
• C. They react with oxygen to form peroxides
• D. They are best prepared in aqueous solvents

Answer: (B)

Grignard reagents are highly reactive organomagnesium halides that must be formed and used under strictly anhydrous, oxygen-free conditions. Any trace of water or exposure to air immediately reacts with RMgX, quenching it or causing decomposition, so you get hydrocarbons and Mg salts instead of the intended reagent. That is why the preparation and use rely on dry solvents (like diethyl ether or THF) and an inert atmosphere.

This is the best statement because it captures the essential practical requirement for working with Grignard reagents: moisture and air must be excluded. In contrast, they are not stable in water, they are not prepared in aqueous solvents, and although reaction with oxygen can lead to side processes such as peroxide formation, the defining practical rule for making and handling them is maintaining anhydrous, oxygen-free conditions.