Grignard reagent synthesis is always carried out in dry ether because
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Grignard reagent forms hydrocarbon with water
In a Grignard reagent, R–MgX, the C–Mg bond is covalent but highly polar, with carbon carrying a partial negative charge. R therefore behaves as a carbanion and takes a proton from any proton source, even water, giving the hydrocarbon:
\( \displaystyle \ce{RMgX + H2O -> RH + Mg(OH)X} \)
Even traces of moisture would destroy the reagent, so it is prepared and used in dry ether.
Why the other options are incorrect
Option (1) Alkyl halides are highly soluble in water — Incorrect. Alkyl halides are only very slightly soluble in water, and their solubility is not the reason for avoiding water.
Option (2) \(Mg\) metal is more stable in dry ether — Incorrect. Magnesium metal is not decomposed by moist ether; it is the Grignard reagent formed from it that reacts with water.
Option (3) \(Mg-X\) bond is extremely covalent — Incorrect. The magnesium–halogen bond is essentially ionic; the covalent but polar bond is C–Mg.
NCERT (2026-27 edition):
Reaction with Metals – “… In the Grignard reagent, the carbon-magnesium bond is covalent but highly polar, with carbon pulling electrons from electropositive magnesium; the magnesium halogen bond is essentially ionic. Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons. Even water, alcohols, amines are sufficiently acidic to convert them to corresponding hydrocarbons. It is therefore necessary to avoid even traces of moisture from a Grignard reagent. That is why reaction is carried out in dry ether.”