Step-by-step explanation:
Metal oxides are generally basic in nature.
When metal oxides react with acid they form respective metal salt and water.
Acid + Metal Oxide => Salt + Water
Neutralization Reaction :
Acid + Base => Salt + Water
This is similar to neutralization reaction where base comes instead of Metal oxide. Hence it can be concluded that Metal oxide is a base.
So Bases turn Red litmus to blue.
Hence the solution of any metal oxide will turn Red litmus to Blue but it has no effect on the Blue Litmus paper.