Ions have a negative or positive charge because silver is metal. It is a cation (Ion with a positive charge).
The answer is (3) pH 3 to pH 1. The pH is related to the concentration of H3O+ with the relationship: pH = -lg c(H+). So when concentration of H3O+ increase, the pH will decrease. And decrease 2 when when increase hundredfold. Because 100=10^2.
Iron (II) oxide is composed of iron with an oxidation number of +2 (shown by the II after iron) and an oxygen that has an oxidation number of -2 (oxygen almost always has an oxidation state of -2). Since the anion and cation both have a charge of +or- 2, they bond with each other with a 1 to 1 ratio and the formula should be FeO
I hope this helps. Let me know if anything is unclear.
