Classify the below substances based on their natural physical state (Solid or Gas).
Methane, Gold, Silver, Platinum
Solid - old, Silver, Platinum
Gas - Methane
<START_INST>Classify the below substances based on their natural physical state (Solid or Gas).
Methane, Gold, Silver, Platinum<END_INST><START_CTX><END_CTX><START_A>Solid - old, Silver, Platinum
Gas - Methane<END_A>