Molar mass NaOH = 39.997 g/mol
number of moles solute:
n = mass of solute / molar mass
n = 30 / 39.997
n = 0.00075 moles of NaOH
Volume in liters:
500 mL / 1000 => 0.5 L
Therefore :
M = moles of solute / volume ( L )
M = 0.00075 / 0.5
M = 0.0015 mol/L
