The idea of planetary electron was that of A.Rutherford B.Thompson C.Bohr D.Dalton

To determine which scientist is associated with the idea of planetary electron, we can evaluate the contributions of each scientist listed:

1. A. Rutherford - Proposed the nuclear model of the atom, which describes the atom as having a nucleus at its center with electrons orbiting around it, similar to planets orbiting the sun. This concept laid the groundwork for the planetary model of the atom.

2. B. Thompson - Known for the discovery of the electron and proposed the "plum pudding" model of the atom, where electrons are embedded within a positively charged "soup." This model does not accurately reflect the planetary structure.

3. C. Bohr - Developed the Bohr model of the atom, which further refined Rutherford's idea by introducing quantized orbits for electrons, but he is more known for detailing how electrons can occupy fixed energy levels rather than just the concept of a planetary model.

4. D. Dalton - Proposed the atomic theory, which focused on the idea of atoms as indivisible units and did not specifically address the arrangement of electrons around the nucleus.

Final Answer

The scientist associated with the idea of the planetary electron is A. Rutherford.