Question

What type of oxides are formed when non-metals combine with oxygen?

Answer 1

When non-metals combine with oxygen, the oxides of non-metals are formed.
For example, $S+O_2⟶S{O}_2$

Here sulphur is a non-metal which combines with oxygen gas to form sulphur dioxide. When this sulphur dioxide is dissolved in water sulphurous acid is formed.

$S{O}_2+H_{2}O⟶H_{2}S{O}_3$

This sulphurous acid can turn blue litmus paper red. This indicates that oxides of non-metals are acidic in nature.