Question

the reduction half - reaction shows the need for two more oxygen atoms on the product side. will you add water or hydroxide to the product side?
mno₄⁻ → mno₂ + ?
a. water b. hydroxide
enter the answer choice letter.

Explanation:

In a reduction half - reaction, when we need to balance oxygen atoms, if the reaction is in a basic or neutral medium (or we can also consider the general approach for balancing redox half - reactions), to add oxygen atoms, we add water ($H_2O$) when we need to add $O$ atoms. The half - reaction here is $MnO_4^-\to MnO_2 + [?]$. The reactant $MnO_4^-$ has 4 $O$ atoms and the product $MnO_2$ has 2 $O$ atoms. We need to add 2 $O$ atoms to the product side. Water ($H_2O$) has one $O$ atom per molecule, and adding water will provide the necessary oxygen. Hydroxide ($OH^-$) does not provide oxygen in the same way for this kind of oxygen - balancing in a half - reaction (it is more related to balancing hydrogen and charge in basic media after oxygen is balanced with water). So we add water to the product side.

Answer:

B