The order of reactivities of methyl halides in the formation of grignard reagent is
methyl chloride is less than methyl bromide is less than methyl iodide.
Grignard reagents are highly reactive and react with any source of a proton to give hydrocarbons. Water, alcohol, amines are sufficiently acidic to convert them to corresponding hydrocarbons. Halide reactivity increases in the order Cl<Br<I