To determine which compound undergoes racemization when hydrolyzed with KOH, we need to identify the presence of a chiral center.$\\$Racemization occurs when a chiral center is converted into a racemic mixture, typically through an $S_N1$ mechanism.$\\$Let's analyze each compound:$\\$(a) Benzyl chloride (C$_6$H$_5$CH$_2$Cl):$\\$• The carbon attached to Cl is not chiral (no four different groups).$\\$• Does not undergo racemization.$\\$(b) 1-Chloropropane (CH$_3$CH$_2$CH$_2$Cl):$\\$• The carbon attached to Cl is not chiral.$\\$• Does not undergo racemization.$\\$(c) 2-Chlorobutane:$\\$• The carbon attached to Cl is chiral (attached to four different groups: CH$_3$, CH$_2$CH$_3$, H, Cl).$\\$• Can undergo racemization through an $S_N1$ mechanism.$\\$(d) 2-Chloro-2-methylbutane:$\\$• The carbon attached to Cl is chiral (attached to four different groups: CH$_3$, C$_2$H$_5$, H, Cl).$\\$• Can undergo racemization through an $S_N1$ mechanism.$\\$Conclusion:$\\$• Compounds (c) and (d) have chiral centers and can undergo racemization.$\\$Therefore, the correct option is (c) and (d), which corresponds to Option 3.