Step 1
A mole fraction is defined as:
Mole fraction (compound X) = moles of compound X/total moles
It has no units
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Step 2
The solution is formed by solute and solvent. Therefore, the total moles will be:
0.589 moles NaCl + 0.625 moles water = 1.214 moles
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Step 3
Molar fraction (NaCl) = moles NaCl/total moles = 0.589 moles/1.214 moles = 0.49 approx.
Answer: Molar fraction of NaCl = 0.49