For Q (C4H9Cl) to be optically active, it must have a chiral center.
P (C4H8) = but-2-ene (CH3−CH=CH−CH3)
P + HCl → Q: CH3−CH=CH−CH3+HCl→CH3−CH(Cl)−CH2−CH3 (2-chlorobutane, chiral at C-2)
Q + NH3 → R: 2-chlorobutane + NH3→CH3−CH(NH2)−CH2−CH3 (2-aminobutane)
R → diazotization → hydrolysis → S: 2-aminobutane NaNO2/HCl diazonium salt H2O CH3−CH(OH)−CH2−CH3 (butan-2-ol)



