The compound showing complete stereochemical inversion during an S_N2 reaction is:

The major product of the following reaction is:

The increasing order of reactivity of the following compounds towards reaction with alkyl halides directly is:

$\left(i\right)$

$\left(ii\right)$

$\left(iii\right)$

$\left(iv\right)$

The major product of the following reaction is:

In the reaction given below what will be the major product at the end :

The reagent required for the following two step transformation are

The major product of the following reaction is: