Step 1: Understanding the Concept
Some drugs are named after the element they contain.
Step 2: Check each drug
Prontosil is a sulfonamide dye.
Chloramphenicol contains chlorine.
Thymol is a phenol derivative.
Salvarsan (arsphenamine) contains arsenic.
Step 3: Conclude
Salvarsan is the arsenic-containing antibiotic.
Final Answer:
Salvarsan is the antibiotic containing arsenic.
\[ \boxed{\text{(C) }\text{salvarsan}} \]