What could J. J. Thomson conclude from his experiments?

A) Atoms are mostly empty space.

B) Most of the mass of the atom is concentrated in the center.

C) Atoms must balance positive and negative particles.

D) Atoms are indivisible.

The most accurate answer would be letter B. From the series of experiments that he conducted inside his laboratory, J. J. Thomson could conclude that most of the mass of an atom is concentrated in its center, or the area where most of the parts of an atom such as the nucleus, etc ... are situated.