Question

how long ago did the history of understanding the atom begin?
a 100 years ago
b 500 years ago
c 1500 years ago
d 2500 years ago

Explanation:

The concept of the atom was first proposed by the ancient Greek philosopher Democritus around 2500 years ago. He theorized that matter was composed of indivisible particles called atoms.

Answer:

D. 2500 years ago