Question

how many molecules and atoms of phosphorus are present in 0.1 mole of P4 molecules?

Answer 1

number of molecules = number of moles × Avogadro's constant .

no of molecules = 0.1 × 6.023 × 10²³

= 6.023 × 10²²

in P4
no of atoms = 4 × no of molecules
so,
no of atoms = 4 × 6.023 × 10²²

= 24.092 × 10²²

Answer 2

You know that in 1 mole of p4 there are 4 moles of p  

Similarly in .1 moles of p4 there are .4 moles of p  

So number of atoms = 4/10*6*10^23  

Therefore number of atoms = 2.4*10^23