What is the total number of naturally occurring elements?

Atomic mass of an element is equal to the sum of number of

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?

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