A sample of ammonium phosphate, (NH4)3PO4, contains 0.104 mol of nitrogen atoms. The number of moles of oxygen atoms in the sample is

There are 0.1387 moles of oxygen atoms.

Explanation:

First we calculate how many moles of ammonium phosphate there are:

Finally we calculate how many moles of oxygen atoms are there in 0.312 moles of (NH₄)₃PO₄:

Thus there are (0.0347 mol (NH₄)₃PO₄ * ) 0.1387 moles of O.