Final answer:
The first ancient Greek philosopher to propose the notion of the atom was Democritus, with the aide of Leucippus. They conceived the atom as indivisible, in constant motion, and each distinguishable in size and shape. These concepts led to the foundation of the atomic theory which guides modern understanding.
Step-by-step explanation:
The ancient Greek natural philosopher who first proposed the notion of the atom was c) Democritus. He, together with Leucippus, formulated the idea of atomos in the 5th century BC, meaning 'indivisible.' These philosophers believed that everything is composed of these tiny, finite particles that could join together. They envisioned atoms as diverse in size and shape and capable of being in constant motion. However, they never proceeded with conducting experiments to validate their ideas.
This idea raised a fundamental question: whether one can infinitely divide a substance into smaller pieces or whether there exists a smallest unit which cannot be further subdivided. Democritus notably proposed this latter view, introducing the concept of the 'atom.'
Though we now know that atoms can be broken down further, the essence of the atomic theory as initiated by Democritus and Leucippus holds accurate. The Greek philosophers' initial conception of the atom forms an important part of the history of atomic theory and continues to guide our understanding of the microscopic world.
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