Question

How many moles of Oxygen are present in 0.1 moles of H3PO4?​

Answer 1

since one molecule of H3PO3 contains 3 atoms of hydrogen, 1 atom of P and 4 atoms of O so 1 mole of H3PO4 will contain 3 moles of H, 1 mole of P, 4 moles of O.

if you you are looking for total moles of H,O,P in 1 mole of H3PO4 then the answer will be 8 moles.