If electronegativity difference between atoms is much higher then they form ionic bond.
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In a reduction-oxidation or better known as REDOX reaction, the substance that reduces the oxidation state is known as the substance that is REDUCED. It serves as the oxidizing agent. Thus, Au3+ in this number is considered as the oxidizing agent.
Answer:
mol times or devided by molar volume
Hydrogen because it only has one electron
