Final answer:
The amount of Oxygen gas needed for the reaction to follow the Law of Conservation of Mass is 26.42g.
Step-by-step explanation:
To determine the amount of Oxygen gas needed for the reaction to follow the Law of Conservation of Mass, we need to compare the molar masses of the reactants and products.
From the given equation, 2NO₂ --> 2NO + O₂, the molar mass of NO₂ is 46 g/mol and the molar mass of O₂ is 32 g/mol. This means that for every 46 grams of NO2, 32 grams of O₂ are needed for the reaction to be balanced.
Therefore, the correct answer is B) 26.42g.