Answer: The correct answer is Option a.
Explanation:
J.J Thomson was a scientist who gave the existence of two subatomic particles which are protons (positive particles) and electrons (negative particles).
He proposed a model which was known as plum pudding model.
He considered atom to be a pudding or bed of positive charge in which negative particles are embedded such as plum on the pudding.
Hence, the correct answer is Option a.