The value of pH determines how acidic or basic a solution is. There are chemicals that change colour at different pH values. These are called indicators . One of the most famous is Litmus . Oxides Oxides are compounds containing Oxygen.
Oxides can be Acidic, Basic or Neutral.
Acidic Oxides react with water to form an acid. NO and NO 2 . Basic Oxides react with water to form an alkali. Most metal oxides are basic. Amazon COM Amazon Co UK Organic Chemistry is a good book for the undergraduate.