38.5 mol of p4o10 contains how many moles of p?

The subscripts tell the ratio of one element to another in a compound. In this case, there are 4 P atoms per 10 O atoms. This could also be interpreted as 4 mol P per 10 mol O. Therefore:

Mol P = (38.5 mol P4O10)/(4 mol P/ 1 mol P4O10) = 154 mol P 

i had this on my unit activity, i can you if you are a plato student. are you a plato student?

im pretty sure its b