To find the number of neutrons in an atom you can use and equation
N = Mass no. - Protons
N of chlorine-36 = 36 - 17 = 19
so chlorine-36 has 19 neutrons
hope that helps
He proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another.
The correct answer would be the last option. The property that is common to all group 2 elements is that they tend to form ionic bonds by losing electrons making these atoms positive charge. They are called cations. These elements are beryllium, magnesium, calcium, strontium, and radium.