Respuesta :
The reaction equation of this is NaOH + HCl = NaCl + H2O. So the mol number of NaOH and HCl are the same. So we can get equation: 40*0.5=10*[NaOH]. (both side of equation is using the same unit of volume) [NaOH]=2.0 M. The answer is (2) 2.0 M.