`NaOH+HCl rarr NaCl+H_2O`
Amount of HCl moles reacted `= 2/1000xx18.5 = 0.037`
Since the mole ration between NaOH and HCl is 1:1 we should have 0.037moles of NaOH in the solution.
Molarity is the concentration of a solution in mol/L
Let us say the molarity of the NaOH solution is Mmol/L.
`M/1000xx21.2 = 0.037`
`M = 1.745`
So the molarity of the NaOH solution is 1.745mol/L