Who discovered radioactivity?

• A. Henri Becquerel
• B. Marie Curie
• C. Louis Pasteur
• D. Albert Einstein

Answer: (A)

The main idea is that some materials can emit radiation on their own, without any external trigger. Henri Becquerel showed this first in 1896 by using a uranium-containing substance and a photographic plate. He kept the setup in the dark and found the plate fogged, meaning the uranium emitted radiation by itself, not because of light or heat. This demonstrated a new, spontaneous source of radiation and established Becquerel as the discoverer of radioactivity. Marie Curie built on that work, conducting systematic measurements and identifying new radioactive elements like polonium and radium. The other names didn’t relate to the discovery: Pasteur is known for microbiology, and Einstein contributed to theories of light and energy but did not discover radioactivity.