<p>What is the&nbsp;<math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="[" close="]"><mrow><mi>O</mi><msup><mi>H</mi><mo>-</mo></msup></mrow></mfenced></math>&nbsp;in the final solution prepared by mixing 20.0 mL of 0.050 M HCI with 30.0 mL of 0.10 M Ba<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mfenced><mrow><mi>O</mi><mi>H</mi></mrow></mfenced><mn>2</mn></msub></math>?</p>