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.