<u>Answer:</u> The chemical reaction for the synthesis reaction is given below.
<u>Explanation:</u>
Synthesis reaction is defined as a chemical reaction in which two small chemical substances combine together to form a single compound. The general equation for this chemical reaction follows:

For the reaction of calcium and oxygen combining together to form calcium oxide, the equation follows:

By Stoichiometry,
2 moles of calcium element combines together with 1 mole of oxygen gas to produce 2 moles of calcium oxide.
Hence, the chemical equation for the reaction is given above.
Answer: (Chlorine-35)
Element X is Ca
Explanation:
Number of proton plus the number of electron gives the mass number.
Explanation is in a file
bit.
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There can be three mole ratios that can be written involving three substances.It depends on the constant of your reactant to your product. It also depends on the asked mole ratio. But the maximum would be 3 mole ratios because you have 3 substances in your reaction.