Here's how to calculate the mole fraction of NaCl in the solution:

1. Calculate the total moles:

* Moles of NaCl = 18 mol

* Moles of water (H₂O) = 100 g / 18.015 g/mol ≈ 5.55 mol

(We use the molar mass of water to convert grams to moles)

* Total moles = 18 mol + 5.55 mol ≈ 23.55 mol

2. Calculate the mole fraction of NaCl:

* Mole fraction of NaCl = (Moles of NaCl) / (Total moles)

* Mole fraction of NaCl = 18 mol / 23.55 mol ≈ 0.764

Therefore, the mole fraction of NaCl in the solution is approximately 0.764.