Among the following, the number of tranquilizer/s is/are ______
A. Chlorodiazepoxide
B. Veronal
C. Valium
D. Salvarsan

We need to identify the tranquilizers from the given options.

A. Chlorodiazepoxide: This is a benzodiazepine derivative used as a tranquilizer. It was the first benzodiazepine to be discovered (marketed as Librium).

B. Veronal: Veronal (barbital/barbitone) is a barbiturate used as a hypnotic/sedative, not classified as a tranquilizer. It is a sleep-inducing drug (hypnotic).

C. Valium: Valium (diazepam) is a benzodiazepine and is a well-known tranquilizer.

D. Salvarsan: Salvarsan is an organoarsenic compound used as an antimicrobial/antisyphilitic drug. It is not a tranquilizer.

Chlorodiazepoxide and Valium are tranquilizers. That gives us 2 tranquilizers.

The correct answer is 2.