find out the mass number of oxygen and sulphur atom.

For the following statements, write $T$ for True and $F$ for False.

$(a)$ J.J. Thomson proposed that the nucleus of an atom contains only nucleons.

$(b)$ A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.

$(c)$ The mass of an electron is about $\frac {1}{ 2000}$ times that of proton.

$(d)$ An isotope of iodine is used for making tincture iodine, which is used as a medicine.

Compare the properties of electrons, protons and neutrons.

Helium atom has an atomic mass of $4\,u $ and two protons in its nucleus. How many neutrons does it have ?

Describe Bohr’s model of the atom.