1) a) At 20°C, Y is in a solid state. b) At 250°C, Y is in a gaseous state.
2) The state symbol for Y in a symbol equation would depend on the temperature and pressure conditions of the reaction. If Y is in a solid state, (s) would be used. If Y is in a liquid state, (l) would be used. If Y is in a gaseous state, (g) would be used.