What is the molarity of 3.5 wt % NaCl dissolved in 1000 mL of distilled water?
You cannot determine it from the information given.
To determine the number of moles of solute, you need to divide the mass of substance that has been dissolved by its molar mass.
But the question does not tell you what the name of the substance or its molar mass. So it is not possible to work out the number of moles, and therefore you cannot work out the molarity.
The molar concentration is 0.61 mol/L.
Assume you have 1000 g of the solution.
Step 1. Calculate the mass of each component
Step 2. Calculate the volume of the solution
I shall assume that the density of the solution 1.023 g/mL. Then
Step 3. Calculate the moles of
Step 4. Calculate the molar concentration of