A trinitro compound, 1,3,5 tris-(4-nitrophenyl) benzene, on complete reaction with an excess of Sn/HCl gives major product, which on treatment with an excess of  $NaN{O}_2/HCl$ at $0°C$ provides P as the product, P, upon treatment with excess of $H_{2}O$ at room temperature gives the product Q. Bromination of Q in aqueous medium furnishes the product R. The compound P upon treatment with an excess of phenol under basic conditions gives the product S.
The molar mass difference between compounds Q and R is $474mo{l}^{-1}$ and between compounds P and S is  $172.5gmo{l}^{-1}$ $[H=1,C=12,N=14,\text{\hspace{0.17em}}O=16,Br=80,Cl=35.5]$