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

We need to identify which of the given compounds are tranquilizers.

A. Chlorodiazepoxide: This is a benzodiazepine derivative, which is a well-known tranquilizer. It was one of the first benzodiazepines to be synthesized and is used to treat anxiety and tension. Yes, it is a tranquilizer.

B. Veronal: Veronal (barbital) is a barbiturate. Barbiturates act as central nervous system depressants and are classified as tranquilizers/hypnotics. They are used to induce sleep and reduce anxiety. Yes, it is a tranquilizer.

C. Valium: Valium (diazepam) is another benzodiazepine and is one of the most widely known tranquilizers. It is used to treat anxiety disorders, muscle spasms, and seizures. Yes, it is a tranquilizer.

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

Conclusion: Out of the four compounds, three (A, B, and C) are tranquilizers.

The answer is $$\textbf{3}$$.