To find the mole fraction of water in the solution, we first need to calculate the total number of moles in the solution:
Total moles = moles of water + moles of ethanol + moles of acetic acid
= 2.5 + 2.5 + 5.0
= 10.0 moles
Now, we can find the mole fraction of water:
Mole fraction of water = Moles of water / Total moles
= 2.5 / 10.0
= 0.25
So, the correct answer is B. 0.25.