Question

how many atoms are in P4?

Answer 1

Well, since we don't have the original mass of P4, I take it you forgot to include that but if not, this is how you can find it.

P4 = Phosphorus = Mass = 30.974 x (4) (Because 4 molecules) = 123.896

(Grams of element)*(Avogadro's Number)/(atomic weight of Element)

123.896 x 6.02x10^23 = 7.45 since we do not have the atomic weight, that would be your final answer, if you gave us P4 original mass, you would just divide 7.45 to get the correct answer.