Answer: the correct answer is option 2.
Explanation:
Electrons are the negatively charged sub-atomic particles which were discovered by J.J Thomson.
After the discovery of electrons, their location was determined. Neil Bohr discovered that the electrons revolved around the nucleus in fixed paths. But their location was yet to be determined.
As the electrons are continuously moving, their fixed location cannot be determined. But, the most probable location of electron was discovered by Erwin Schrodinger. He discovered that the most probable location of an electron is an orbital.
Hence, the correct answer is option 2.