The coefficient in a chemical formula represents the amount of each chemical present. The amount of a substance is measured in moles.
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Explanation:
Copper(II) sulfide reacts with oxygen gas to give solid copper(II) oxide and sulfur trioxide gas.
The reaction is given as:

When 1 mol copper(II) sulfide react with 2 moles of oxygen gas it gives 1 mol of solid copper(II) oxide and 1 mol of sulfur trioxide gas
The gas formed in above reaction that is sulfur trioxide reacts with water to give sulfuric acid or hydrogen sulfate.
The reaction is given as:

1 mol of sulfur trioxide gas reacts with 1 mol of liquid water to produce 1 molo of liquid hydrogen sulfate or sulfuric acid
Answer:
C. Solid
Explanation:
It's most about the kinetic energy, when molecules have the least amount of room to move around, they have the least amount of energy.
For example if you think about gas and how spread out the molecules are in order to evaporate, there it the highest amount of energy there.
Answer:
Valence Electrons are transferred/exchanged