Paragraphs-2
A trinitro compound, \( 1,3,5 \)-tris-(\( 4 \)-nitrophenyl) benzene, on complete reaction with an excess of \( \mathrm{Sn/HCl} \) gives a major product, which on treatment with an excess of \( \mathrm{NaNO_2/HCl} \) at \( 0^\circ \text{C} \) provides \( P \) as the product. \( P \), upon treatment with excess of \( \mathrm{H_2O} \) 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 \( 474 \, \text{g mol}^{-1} \) and between compounds \( P \) and \( S \) is \( 172.5 \, \text{g mol}^{-1} \).
The number of heteroatoms present in one molecule of \( R \) is ___________.
[Use : Molar mass (in \( \text{g mol}^{-1} \)): \( \mathrm{H} = 1 \), \( \mathrm{C} = 12 \), \( \mathrm{N} = 14 \), \( \mathrm{O} = 16 \), \( \mathrm{Br} = 80 \), \( \mathrm{Cl} = 35.5 \) ; Atoms other than \( \mathrm{C} \) and \( \mathrm{H} \) are considered as heteroatoms]
