What is the number of atoms in 46 g of sodium-23 (N = Avogadro constant)?

What is the number of moles of ‘He’ in 104 g of helium gas?

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

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

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

The atoms, in which the number of protons is same but the number of neutrons is different, are known as –