Question 3

Step 1: L-Glucose reacts with $HI$ and red phosphorus on heating to undergo complete reduction, forming n-hexane.

Step 2: n-hexane undergoes aromatization in the presence of $Cr_2O_3$ at $775 K$ and high pressure to form Benzene ($P$).

$CH_3(CH_2)_4CH_3 \xrightarrow{Cr_2O_3, \Delta} C_6H_6 (P)$

Step 3: Benzene reacts with excess $Cl_2$ in the presence of UV light via a free radical addition reaction to form Benzene Hexachloride (BHC), also known as Gammexane or Lindane.

$C_6H_6 + 3Cl_2 \xrightarrow{UV} C_6H_6Cl_6 (Q)$

Structure (D) in the paper represents 1,2,3,4,5,6-hexachlorocyclohexane. Hence, the correct option is (D).