The type of oxides formed when metals combine with oxygen are

When metals combine with oxygen, they typically form basic oxides. These oxides exhibit basic properties, such as reacting with water to produce hydroxides or with acids to form salts and water in neutralization reactions. For example, sodium oxide reacts with water to produce sodium hydroxide:

Na₂O+H₂O→2NaOH

This reaction illustrates the basic nature of metal oxides.

Therefore, the correct answer is: a) Basic oxides