Composition of the nuclei of two atomic species, X and Y, are given as under

Give the mass numbers of X and Y. What is the relation between the two species?

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 $\dfrac{1}{2000}$ times that of a proton.

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

Isotopes of an element have

1. The same physical properties
2. Different chemical properties
3. Different number of neutrons
4. Different atomic numbers

Number of valence electrons in Cl^- ion are

1. 16
2. 8
3. 17
4. 18