According to the law of conservation of mass, mass is neither created nor destroyed in any ordinary chemical reaction. Which of the following is a demonstration of this law? Group of answer choices a. When iron reacts with oxygen to form rust, the mass of the iron atoms increases. b. When carbon dioxide breaks down into carbon and oxygen, the number of atoms always remains the same. c. When sodium and chlorine combine to make salt, some of the sodium is always lost. d. When hydrogen and oxygen combine to make water, oxygen atoms are converted to hydrogen atoms.

Option A is wrong because mass cannot be created, so there should be no increase. Option C is wrong because mass cannot be destroyed, so there should be no loss of mass. Option D is wrong because oxygen atoms and hydrogen atoms have different masses, so oxygen being converted to hydrogen would result in a loss of mass. In Option B, the number remains the same.

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