Q. Who was the first one to propose a model for the structure of an atom ?

Correct Answer: d) J. J. Thomson

Explanation:
J. J. Thomson was the first to propose a model for the structure of an atom. In 1897, after discovering the electron, he proposed the “Plum Pudding Model” of the atom. According to this model, the atom was envisioned as a sphere of positive charge in which negatively charged electrons were embedded, much like raisins in a pudding or seeds in a watermelon.

The other options are incorrect because:
– a) E. Goldstein: He discovered canal rays (positively charged particles) but did not propose a model for the atom.
– b) Rutherford: He proposed the nuclear model of the atom in 1911, which came after J. J. Thomson’s model. Rutherford’s model suggested that the atom has a dense, positively charged nucleus with electrons orbiting around it.
– c) Neils Bohr: He refined Rutherford’s model in 1913 by introducing the concept of quantized electron orbits, leading to the Bohr model of the atom.

Thus, J. J. Thomson was the first to propose a model for the structure of an atom.