Decomposition reaction results in the formation of the products by splitting the reactants. Moles of mercury(ii) oxide needed are 15.63 moles.
<h3>What are moles?</h3>
Moles are the ratio of mass and the molar mass of the compound or the molecule.
Moles of oxygen are calculated as:

The balanced chemical reaction can be shown as,

From the reaction, it can be said that 1 mole of oxygen requires 2 moles of mercury oxide.
Moles of mercury oxide are calculated as:

Therefore, option C. 15.63 moles of mercury (II) oxide is needed.
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brainly.com/question/26898237
Answer is: the oxidation number of oxygen must decrease.
Oxidizing agent is element (substance) that gain electrons in chemical reaction.
For example, balanced chemical reaction: C + O₂ → CO₂.
Oxygen change oxidation number from 0 to oxidation number -2 (reduction) and carbon change from 0 to +4 (oxidation)
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the mass of 1 mole of the element is used as a conversion factor to convert grams to moles