Compound IV undergoes inversion of configuration
The order of reactivity for I, III and IV is: IV>I>III
I and III follow SN1 mechanism
I and II follow SN2 mechanism
The statements (A), (B) and (C) are correct (A) I and III follow SN1 mechanism. They lose bromide ion to form stable carbocations. Benzylic carbocation is stabilised by resonance with aromatic nucleus. Tertiary carbocation is stabilised due to inductive effect of 3 methyl groups.