Question

What is the mole fraction of ethanol in a solution of 3.00 moles of ethanol and 5.00 moles of water?

Answer 1

If theres a mixture of components we can calculate the mole fraction
mole fraction can be calculated as follows
mole fraction of component = $\frac{number of moles of component}{total number of moles of all components }$
number of moles of ethanol - 3.00 mol
total number of moles in mixture - 3.00 + 5.00 = 8.00 mol 

mole fraction of ethanol = $\frac{3.00 mol}{8.00 mol }$
mole fraction of ethanol is 0.375