For questions about Grignard reagents RMgX (R = alkyl/aryl/vinyl, X = halide): their chemical and physical properties and reactions.

Grignard reagents are used in addition reactions in organometallic chemistry. They are alkyl-, vinyl-, or arylmagnesium halides, which readily add to a carbonyl group in aldehydes or ketones. These reactions are important tools for the formation of carbon–carbon bonds.

A Grignard reagent has a formula $\ce{RMgX}$ where $\ce{X}$ is a halogen, and $\ce{R}$ is an alkyl or aryl (based on a benzene ring) group. A typical Grignard reagent is $\ce{CH3CH2MgBr}$.

Grignard reagents are usually stored in dry ether, because the lone pair coordinated from the oxygen atom of ethers completes the octet of magnesium. Care should be taken not to introduce water which would hydrolyse the Grignard reagent rapidly.

More so, the R- group in Grignard cannot contain $\ce{-OH}$, $\ce{-NH2}$, and other such groups with acidic hydrogens, which would otherwise quickly react with themselves.

Reference can be your own text book, Wikipedia and IUPAC Gold Book.