Molarity or molar concentration is a measure of the concentration of a chemical species, of a solute in a solution, using as units, number of moles, and volume in liters. The formula for Molarity is:
M = n/V
Where:
n = number of moles
V = volume in Liters
But in this case, we don't have the number of moles, therefore we need to use the given mass of NaOH, 5.68 grams, and its molar mass, 40g/mol in order to find the number of moles:
40g = 1 mol
5.68g = x moles
40x = 5.68
x = 5.68/40
x = 0.142 moles of NaOH in 5.68 grams
Now we can use the Molarity formula:
M = 0.142/0.400
M = 0.355
The molarity of this solution is 0.355 M