Chlorine occurs in nature in two isotopic forms of masses 35 u and 37 u in the ratio of 3 : 1 respectively. What is the average atomic mass of the Chlorine atom ?

The number of electrons and neutrons in an element is 18 and 20 respectively. Its mass number is

What is the mass number of an element, the atom of which contains two protons, two neutrons and two electrons?

The two isotopes of elemental chlorine are :

Number of electrons present in the species H₂⁺, He, H and O₂⁺ respectively are :

What is the maximum number of electrons that can occupy the first shell of an atom ?