According to the law of conservation of mass, the total mass of the reactants must equal the total mass of the products in a chemical reaction.
In this case, you have:
- 24 grams of magnesium
- 16 grams of oxygen
To find the total mass of the reactants, you add these two amounts together:
\[ \text{Total mass of reactants} = \text{mass of magnesium} + \text{mass of oxygen} \] \[ \text{Total mass of reactants} = 24 , \text{g} + 16 , \text{g} = 40 , \text{g} \]
Therefore, the mass of magnesium oxide produced will also be 40 grams after the reaction is complete.
The answer is B. 40 g.