The molar mass of NaOH is 40 g/mol.
The number of moles of NaOH is equal to the ratio of its mass to molar mass.
The number of moles of NaOH =
40g/mol
40g
=1mol
The molarity of NaOH solution is the ratio of number of moles of NaOH to total volume of solution in L.
M=
1L
1mol
=1M
