To make a solution of pH = 12, the amount of NaOH dissolved in one liter of the solution should be

pH = 12  ; POH =14-12= 2or      OH-=10-2 Mor     NaOH=10-2 moles/lit                           No. moles(n) =wGmw W=10-2× 40 = 0.4 g L-1