What type of oxides are formed when nonmetals combine with oxygen?

Answer

When non-metals react with oxygen, they form oxides which are either acidic or neutral in nature.

For example, 

1. Acidic Oxide

Carbon +Oxygen → Carbon Dioxide

C(s) + O ₂ (g)  → CO ₂ (g)

• Carbon Dioxide dissolves in water to form Carbonic Acid.
• So, Carbon Dioxide is acidic in nature

2. Neutral Oxide

Carbon reacts with Oxygen in an insufficient supply of air to produce Carbon Monoxide .

Carbon +Oxygen → Carbon Monoxide

C (s) + ½ O ₂ (g) → CO (g)

• It does not react with water.
• So, it produces neither acid nor base with water .

Therefore, carbon monoxide is neutral.