Answer:
3.98 g
Explanation:
Step 1. Write the balanced chemical reaction. In this case, magnesium reacts with oxygen to produce magnesium oxide:

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Step 2. Calculate the number of moles of magnesium:

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Step 3. Calculate the number of moles of oxygen:

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Step 4. Identify the limiting reactant comparing the equivalents. Equivalent of Mg:

Equivalent of oxygen:

Therefore, Mg is the limiting reactant.
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Step 5. According to the stoichiometry of this reaction:

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Step 6. Convert the number of moles of MgO into mass:

Answer:
X = Water (H2O) ; Y = Hydrogen ; Z = Oxygen
Explanation:
2(H2O) -------> 2H2 + O2
I am sure the answer is D
Density is mass over volume, so:
14.3/8.46≈ 1.6903 g/cm^3