<u>Answer:</u> The theoretical yield of manganese dioxide is 57.42 grams
<u>Explanation:</u>
We are given:
Moles of manganese = 2 moles
Moles of oxygen gas = 2 moles
For the given chemical equation:

By Stoichiometry of the reaction:
3 moles of oxygen gas reacts with 2 moles of manganese
So, 2 moles of oxygen gas will react with =
of manganese
As, given amount of manganese is more than the required amount. So, it is considered as an excess reagent.
Thus, oxygen gas is considered as a limiting reagent because it limits the formation of product.
By Stoichiometry of the reaction:
3 moles of oxygen gas produces 1 mole of manganese dioxide
So, 2 moles of oxygen gas will produce =
of manganese dioxide
To calculate the number of moles, we use the equation:

Molar mass of manganese dioxide = 87 g/mol
Moles of manganese dioxide = 0.66 moles
Putting values in above equation, we get:

Hence, the theoretical yield of manganese dioxide is 57.42 grams