Observe the following reactions. The order of reactivity of $x, y, z$ towards $S_{N}1$ reaction is:

Compound $A$ with molecular formula $C_4H_9Br$ is treated with aqueous $KOH$ solution. The rate of this reaction depends upon the concentration of compound $A$ only. When another optically active isomer $B$ of this compound was treated with aqueous $KOH$ solution,the rate of reaction was found to be dependent on the concentration of both the compound and $KOH$.
$(i)$ Write down the structural formula of both compounds $A$ and $B$.
$(ii)$ Out of these two compounds,which one will be converted to the product with inverted configuration?

Which among the following will have the highest density?

Predict the product for the following reaction:
$\xrightarrow[\Delta]{alc. \ KOH}$ product

In the $S_{N}2$ substitution reaction $R-Br + Cl^- \xrightarrow{DMF} R-Cl + Br^-$,which of the following will have the highest rate?

Consider the following bromides.
The correct order of $S_N1$ reactivity is