Which of the following was an accidental discovery?

Options

A. Penicillin
B. Insulin
C. Chloramphenicol
D. DNA

Answer

**Step-by-Step Solution:**

1. **Understanding the Question:** The question asks which of the following discoveries was made accidentally. The options provided are penicillin, insulin, chloramphenicol, and DNA.

2. **Analyzing Each Option:**
- **Penicillin:** Discovered by Alexander Fleming in 1928. He noticed that a mold (Penicillium notatum) had contaminated his petri dishes and was killing the surrounding bacteria. This was an accidental discovery.
- **Insulin:** Discovered by Sir Frederick G. Banting and Charles Best in 1921. This was a planned research project aimed at understanding diabetes and its treatment, so it is not an accidental discovery.
- **Chloramphenicol:** Discovered by Mildred C. Rebstock in 1947 from the bacterium Streptomyces venezuelae. This discovery was also intentional and not accidental.
- **DNA:** While James Watson and Francis Crick are credited with the double-helix structure of DNA in 1953, DNA itself was first identified by Friedrich Miescher in the late 1860s. This was a scientific endeavor and not an accidental discovery.

3. **Conclusion:** Based on the analysis, the only accidental discovery among the options is penicillin.

4. **Final Answer:** The correct answer is **penicillin**.

---