Answer:
The correct answer is solid.
Step-by-step explanation:
Based on the given information, it is evident that at 1 atm pressure and 49.9 degrees C the melting of the sample takes place, that is, the unknown sample transforms into the liquid at the mentioned temperature. It can also be said that below 49.9 degrees C, the sample stays at solid-state. From all this, we can also state that at temperature 49.9 degrees C, both the liquid and the solid-state of the sample stays at equilibrium.
As one goes higher, that is, above 49.9 degrees C and up to 209.5 degrees C, the sample remains at liquid state. However, the boiling point of the sample is 209.5 degrees C, which shows that the sample becomes gas above 209.5 degrees C. Thus, the sample remains at solid-state below 49.9 degrees C, at liquid state between 49.9 degrees C to 209.5 degrees C, and a gaseous state above 209.5 degrees C. Hence, if the temperature is 0 degrees C, then solid will be the state of matter for the sample.