Which of the following is the most recent addition to the accepted model of the atom?

Atoms are indivisible particles.

Protons are located in the nucleus.

Electrons form a cloud around the nucleus.

Neutrons orbit the nucleus along circular paths.

I think the best answer for this question is the third option. Electrons form a cloud around the nucleus. According to modern physics, electrons are in constant motion around the nucleus and protons. Additionally, electrons, protons and neutrons are considered as hard particles.