What is the major product formed by HI on reaction with

The product formed in the first step of the reaction of


with excess $$\mathrm{Mg/Et_2O}$$ ($$\mathrm{Et=C_2H_5}$$) is

The increasing order of the boiling points of the major products A, B and C of the following reactions will be :

The major product formed in the following reaction is :
CH₃CH = CHCH(CH₃)₂ $$\buildrel {HBr} \over \longrightarrow $$