What is the physical state of water at:
$(a)$ $250\,^{\circ}\text{C}$
$(b)$ $100\,^{\circ}\text{C}$?

(N/A) The boiling point of water is $100\,^{\circ}\text{C}$.
$(a)$ At $250\,^{\circ}\text{C}$,which is above the boiling point,water exists as steam or water vapour,i.e.,in a gaseous state.
$(b)$ At $100\,^{\circ}\text{C}$,water is at its boiling point where a phase transition occurs. Therefore,at this temperature,water exists in both liquid and gaseous states simultaneously.