How many atoms of O are in 4 moles of (NH4)3PO4 - 6H2O?
The answer is 2.41x10^25
I have no clue how to arrive at this answer.
How many molecules of (NH4)3PO4.6H2O are in 4 mols of that stuff?
You know there are 6.02E23 molecules in 1 mol; therefore, there must be 4*6.02E23 molecules in 4 mols.
There are 10 atoms of O in 1 molecule of (NH4)3PO4.6H2O; therefore, there must be 10*4*6.02E23 atoms O in 4 mols of the stuff. Round to 3 significant figures and you get your answer.