According to the law of conservation of matter, the correct statement is that atoms can be rearranged during a chemical reaction, but cannot be created or destroyed. This means that the total number of atoms remains constant before and after a chemical reaction.
To break down the statements you provided:
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Atoms can be rearranged during a chemical reaction, but cannot be added or taken away. - This statement is true and reflects the law of conservation of matter accurately.
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New molecules cannot be formed from the reactants during a chemical reaction. - This statement is false. New molecules can be formed; the atoms simply rearrange to create them.
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The total number of molecules before and after a chemical reaction stays the same. - This statement can be misleading. While the total number of atoms remains the same, the number of molecules can change depending on the reaction.
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Atoms created during a chemical reaction must have the same mass as the atoms in the reactants. - This statement is partially true, as the mass is conserved, but it implies the creation of atoms, which is false. Atoms are not created or destroyed in a chemical reaction; they are rearranged.
So, the first statement is the best reflection of the law of conservation of matter.