How many molecules are in 4.50 moles of h2o?
a. 450 molecules b. 6.02 x 1023 molecules c. 2.71 x 1024 molecules d. 3.00 molecules

C can be the only correct answer - 6.023 x 10^23 is the amount of molecules in a mol of an element. 4.5 x 6.023 x 10^23 can not equal anything but C.

4.5 x 6.023 x 10^23 = 2.71035 x 10^24

They carry out the exchange of gases as we breathe ( oxygen and carbon dioxide).