The answer is temperature (may be wrong)
4 Hydrogen Atoms should be correct. Because the 4 infront of it signifies the amount of hydrogen. It would also be 4 hydrogen atoms if it were written as H4N3, because the 4 is still around the H (as long as the 4 is under scored)
Answer:

Explanation:
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In this case, according to the given information of the solubility of copper chloride, as the maximum amount of this salt one can dissolve without having a precipitate, we infer that since just 73 grams are actually dissolved, the following amount will remain solid as a precipitate:

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CaSO4(s) might be an improperly capitalized: CAsO4(S), CaSO4(S)
Balanced equation:
K2SO4(aq) + CaI2(aq) = CaSO4(s) + 2 KI(aq)
Reaction type: double replacement.