How many moles are in 1.5 x 10^20 molecules of nh3?

Because the question is asking moles of NH3, the compound, any subscripts are irrelevant. It only wants to know how many moles of NH3 molecules, not individual atoms.

Therefore, we can simply convert to moles. 1.5x10^23/6.022x10^23 = .249 moles of NH3.

(If it were to ask moles of Hydrogen, for example, you would multiply the answer by 3, because there are 3 atoms of Hydrogen per one molecule of NH3. But this only asks for moles of the entire compound).  

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