Hi! :)
Ba(OH)2 + 2 HNO3 → Ba(NO3)2 + 2 H2O
(18.2 mL) x (0.45 M Ba(OH)2) x (2 mol HNO3 / 1 mol Ba(OH)2) / (38.5 mL HNO3) = 0.43 M HNO3
Answer:
it will probably flame up or explode or maybe start boiling
The answer is diagram A.
Hope this helped. Good luck!