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

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

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

The number of maximum electrons in N shell is

What is the maximum number of electrons in the M-Shell ?

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