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
<START_INST>Classify the below substances based on their natural physical state.
Water, Mercury, Copper, Oxygen, Nitrogen, Wood<END_INST><START_CTX><END_CTX><START_A>Solid - Copper, Wood
Liquid - Water, Mercury
Gas - Oxygen, Nitrogen<END_A>