The conversation between human and AI assistant.
[|Human|] Classify the below substances based on their natural physical state.
Water, Mercury, Copper, Oxygen, Nitrogen, Wood
[|AI|] Solid - Copper, Wood
Liquid - Water, Mercury
Gas - Oxygen, Nitrogen
[|Human|] 
Classify the below substances based on their natural physical state.
Water, Mercury, Copper, Oxygen, Nitrogen, Wood