What type of oxides are formed when metals combine with oxygen? Explain with the help of an example.

40 What is the nature of the oxide Na₂O? What happens when it is dissolved in water? Write the chemical equation of the reaction involved. 41 What type of oxides are formed when non-metals react with oxygen? Explain with an example. 42 Explain why, metals usually do not liberate hydrogen gas with dilute nitric acid. 42 Name two metals which can, however, liberate hydrogen gas from very dilute nitric acid.