The idea of planetary electron was that of
The correct answer is: A
Explanation
The idea of a "planetary electron," where electrons orbit the nucleus like planets around the sun, is attributed to Ernest Rutherford; his model is often called the "planetary model" of the atom. While Bohr later refined this model by proposing fixed energy levels for electrons, the initial concept of electrons orbiting a central nucleus like planets was put forward by Rutherford.