The equation below shows a general equation for a reaction, and the amounts of the substance are written underneath. AB + CD → AC + BD(15 g) (?) (?) (10 g)The total mass of the products is 50g. Which best completes the other two amounts?

By conservation of mass, the total mass of the reactants equals the total mass of the products: 15 g + CD = 50 g, so CD is 35 g. The products also total 50 g, so AC + 10 g = 50 g, making AC 40 g. Thus, choice B is correct.

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