We can say that oxides, peroxides and superoxides are groups. 1A and 2A are reactive compounds. Now they can react with water to produce hydroxides which are basic in nature and they react with acids to produce salts and water.
If we take a look here, if we have a reacting with water, we have lithium oxide reacting with liquid water, it produces lithium hydroxide base. We put a 2 here to balance it out reacting with acids. Here we have calcium oxide solid reacting with hydrochloric acid that produces our salt in the form of calcium chloride and liquid water.
To balance this we put a 2 with the hydrochloric acid. So just remember when it comes to these oxides, we can react them with water to create bases as a product or it can react them with acids to create water and an ionic compound called a salt.
Li 2 O ( s ) + H 2 O ( l ) → Li 2 OH ( aq ) Ca O ( s ) + 2 H Cl ( aq ) → Ca Cl ( aq ) + H 2 O ( l )