To solve this problem, we need to identify which of the given tranquilizers belongs to the class of barbiturates.$\newline$Barbiturates are a class of drugs that act as central nervous system depressants. They are derived from barbituric acid.$\newline$Let's analyze each option:$\newline$• Option 1: Chlordiazepoxide - This is a benzodiazepine, not a barbiturate.$\newline$• Option 2: Meprobamate - This is a carbamate derivative, not a barbiturate.$\newline$• Option 3: Valium - This is the trade name for diazepam, which is a benzodiazepine, not a barbiturate.$\newline$• Option 4: Veronal - This is the trade name for barbital, which is a barbiturate.$\newline$Therefore, the correct option is Option 4: Veronal.