Which alkyl halide has maximum density?

The organic halide,which does not undergo hydrolysis by $S_{N}1$ mechanism is

$A$ compound $(a)$,$C_8H_9Br$,gives a white precipitate when heated with alcoholic $AgNO_3$. Oxidation of $(a)$ gives an acid $(b)$. The acid $(b)$,$C_8H_6O_4$,easily forms an anhydride on heating. Identify the compound $(a)$.

Which of the following compounds will undergo $S_{N^1}$ reaction most easily?

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

What is the product obtained when $2-$methylpropene is heated with acetyl chloride in the presence of anhydrous $ZnCl_2$?