Answer:
The balanced chemical reaction is :

Explanation:
The precipitation reaction is defined as a chemical reaction in which a solid substance is formed when two aqueous solutions of different compounds are allowed to react with each other.
When an aqueous solution of silver ion and sulfate ions are mixed together solid white precipitate of silver sulfate is formed.
The balanced chemical reaction is written as:

Answer:
Oxygen
Explanation:
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds.
Control or controlled group is the part of the experiment where conditions are kept the same.