According to the Law of Conservation of Mass, the total mass of the reactants must equal the total mass of the products. In this case, you have 2 grams of potassium (K) and 5 grams of oxygen (O).
To find the total mass of the reactants:
\[ \text{Total mass of reactants} = \text{mass of K} + \text{mass of O} = 2 , \text{g} + 5 , \text{g} = 7 , \text{g} \]
Therefore, the mass of potassium oxide (K2O) produced will also be 7 grams.
So the correct response is:
7 grams