Reaction OF carbocation with Base and Nucleophile

General Reaction OF Carbocation with Nucleophile and reaction with Base

Which of the following orders regarding the base strength of a leaving group in a reaction of an acid derivative with a nucleophile is correct :

which is the most stable carbocation formed as intermediate in nucleophilic substitution reaction ?

Rearrangement Reactions OF Carbocations

Since, Grignard reagents resemble carbanion, so they are strong nucleophile and strong base. Their most useful nucleophilic reaction is addition to carbonyl group. Which of the following compounds give racemic mixture on reaction with H_(3)C-MgBr ?

Reaction Mechanism : carbanion,grignard reagent, grignard reagent reaction as base(zero,thOFt reaction) ,grignardre reagant as nucleophilic reaction