Answer:
any atom that contains six protons is the element carbon and has the atomic number 6, regardless of how many neutrons or electrons it may have.
Explanation:
I think because its the only one to be liquid at normal temperatures.
Reaction:

Magnesium is a stronger reducing agent than copper and is thus able to reduce copper(II) oxide.
Products of the reaction: Magnesium oxide and metallic copper.
The protons come from water. Sulfur oxides dissolve in water to form sulfurous and sulfuric acids, and nitrogen oxides dissolve to form nitrous and nitric acids.