The conversion of $\text{RBr}$ to $\text{RMgBr}$ requires:

The synthesis of a Grignard reagent ($\text{RMgBr}$) from an alkyl bromide ($\text{RBr}$) requires metallic magnesium ($\text{Mg}$) in dry ether under an inert gas environment like an **${\text{N}}_2$ atmosphere**.
Dry conditions are absolutely critical because Grignard reagents are highly reactive nucleophiles that undergo rapid protonation and decompose into alkanes when exposed to moisture:

$$\text{RMgBr}+{\text{H}}_2\text{O}\to \text{RH}+\text{Mg(OH)Br}$$

An inert ${\text{N}}_2$ atmosphere is also necessary to prevent side reactions with atmospheric oxygen.