In a neutralization reaction between an acid and the base, the molarity or volume of each can be determined using the equation: M_acid*V_acid = M_base*V_base. The unknown is the M_acid. Using the given values, the equation is M_hno3 = (10*1.67)/20. The result is that the molarity of HNO3 to exactly neutralize the base is 0.835 M.