The amount of substance (mol), which is 18 * 10 ^ 23 water molecules, is …

N = 18 * 10’23 water molecules.
Let’s determine the amount of water substance. For this we use the following formula.
N = n * Na.
N is the number of molecules.
n is the amount of substance.
Na is Avogardo’s number, a constant equal to 6.02 * 10’23.
We express from this formula the amount of substance.
n = N / Na.
Substitute the known values into this expression.
n = 18 * 10’23 / 6.02 * 10 * 23 = 2.99 mol.
This means that the amount of water substance is 2.99 mol.
Answer: the amount of water substance is 2.99 mol.