Classify the below substances based on their natural physical state.
Water, Mercury, Copper, Oxygen, Nitrogen, Wood
Solid - Copper, Wood
Liquid - Water, Mercury
Gas - Oxygen, Nitrogen
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: Classify the below substances based on their natural physical state.
Water, Mercury, Copper, Oxygen, Nitrogen, Wood
### Input: 
### Response: Solid - Copper, Wood
Liquid - Water, Mercury
Gas - Oxygen, Nitrogen