The answer is (3) the most probably location of electrons. (2) and (4) is incorrect because neutrons are found in the nucleus, and the wave-mechanical model defines orbitals as the area of that electron shell with the highest probability of finding an electron. Also, (1) circular path for electrons is incorrect because although circular/spherical orbitals exist (also known as the s orbital), there are many other types of orbitals, such as the p, d, and f orbitals.
