Aglass of water contains 1.2 x 1024 molecules of water. an additional 5.0 moles of water are poured into the glass. how many molecules of water are in the glass?

To answer this question, we convert the number of moles added of water to number of molecules using Avogadro's number, 6.022 x10^23 molecules per mole. 5 moles is equal then to 3.011 x10^24 molecules. we add the initial number of 1.2 x 1024, the total is 4.211 x10^24 molecules. 

The answer is c. 320 g