<span>If thermal energy (heat) must be added to a chemical reaction in order for the reaction to take place, the reaction is endothermic. </span>
"if it is tested in a controlled setting with repeated results" is the statement among the choices given in the question that best describes that can possibly make this scientific claim valid. The correct option among all the options that are given in the question is the first option or option "A". I hope the answer has helped you.<span>
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They become more stable because they achieve a full outer shell of valence electrons with the magic number of 8.
<u>Answer:</u> The additional information that is helpful in calculating the mole percent of XCl(s) and ZCl(s) is the molar masses of Z and X
<u>Explanation:</u>
To calculate the mole percent of a substance, we use the equation:

Mass percent means that the mass of a substance is present in 100 grams of mixture
To calculate the number of moles, we use the equation:

We require the molar masses of Z and X to calculate the mole percent of Z and X respectively
Hence, the additional information that is helpful in calculating the mole percent of XCl(s) and ZCl(s) is the molar masses of Z and X