A scientist named J. J. Thomson developed a model of the atom in which electrons are spread throughout a cloud of positive charge. Which discovery directly caused scientists to revise this model?

A small mass of positive charge was discovered in the center of the atom.

Explanation:

Atoms is the combination of protons, neutrons, as well as electrons particles. The particles that are in the centre of atom is Protons and neutrons, which made up the nucleus, this nucleus is surrounded by electron.

The discovery that directly caused scientists to revise this model of the atom is that A small mass of positive charge known as proton, and a positive charge particle was discovered by Ernest Rutherford, in the center of the atom in the year 1900. Ernest Rutherford through his research resulted to splitting of the atom during nuclear reaction and proton was discovered.