
The reaction proceeds via the formation of a Grignard reagent from alkyl halide (RBr) and magnesium in dry ether, followed by reaction with water to yield 2-methylbutane.
When considering structural isomers of RBr, a maximum of 3 isomers can lead to the formation of 2-methylbutane through this reaction.
The RBr isomers capable of producing 2-methylbutane are:
Therefore, the maximum count of RBr isomers yielding 2-methylbutane is 3.
Write the correct order of rate of reaction of following with PhN$_2$Cl 
Identify A in the following reaction. 