Question

If a box contain 256 water molecules and 1 Na+ ion , then what will be the Molarity of the solution.

Answer 1

I assume you want the molarity of the Na^+. Also, I assume the temerature of the water is such that the density is 1.00 g/mL.

How many mols H2O do we have? That's 256 molecule x (1 mol/6.02E23) = ?
How many grams is that? That's ?mols H2O x (18 g/mol) = ?
How many mL is that? That's
volume in mL = mass/density = ? and convert that to L.

1 Na^+ is how many mols? That's
1 Na^+ x (1 mol/6.02E23) = ?
Then M = mols Na^+/L H2O