The molar concentration of the nitric acid solution was 0.6666 mol/L.
Balanced equation: KOH + HNO_3 → KNO_3 + H_2O
Moles of KOH: 32.33 mL KOH × (1.031 mmol KOH /1 mL KOH)
= 33.33 mmol KOH
Moles of HNO_3: 33.33 mmol KOH× (1 mmol HNO_3/1 mmol KOH)
= 33.33 mmol HNO_3
Concentration of KOH: c = "moles"/"litres" = 33.33 mmol/50.00 mL
= 0.6666 mol/L