State one observation which shows that atom is not indivisible.

Discovery of sub-atomic particles i.e., electrons, protons and neutrons shows that atoms are divisible.

In discharge tube experiment, Goldstein noticed, set of rays travelling in a direction opposite to that of the cathode rays. These were called canal rays since these rays passed through the holes or canals in the cathode. These rays were named positive rays or anode rays. These rays consist of sub-atomic particle proton.