Final answer:
The balanced half-reaction for the oxidation of gaseous arsine to aqueous arsenic acid in basic aqueous solution is AsH3(g) + 3OH-(aq) -> H3AsO4(aq) + 3e-.
Step-by-step explanation:
The balanced half-reaction for the oxidation of gaseous arsine to aqueous arsenic acid in basic aqueous solution is as follows:
AsH3(g) + 3OH-(aq) → H3AsO4(aq) + 3e-
The oxidation state of arsenic in arsine (AsH3) is -3, and it is oxidized to +5 in arsenic acid (H3AsO4). To balance the equation, 3 hydroxide ions (OH-) are added to the reactant side to balance the charge and provide the necessary electrons for the oxidation process.