What is the molar mass of #P_4O_10#?
For such mass related problems we use average mass of elements or compounds. A verge mass of element is dependent on its isotopes and respective fraction found naturally.
In the given question we need to know average mass of Phosphorus and Oxygen.
average mass of Phosphorus P = 30.973762 amu
average mass of Oxygen O = 15.9994 amu
Molar mass of