Phase Diagrams and Clausius-Clapeyron Equation

The vapor pressure of water at 25°C is 23.8 torr and at 100°C is 760 torr. (a) Use the Clausius-Clapeyron equation to calculate the enthalpy of vaporization (ΔHvap). (b) Estimate the boiling point of water at the top of Mount Everest (atmospheric pressure ≈ 253 torr). (c) Explain why the solid-liquid line in the phase diagram of water has a negative slope. (d) What is the triple point and why does it have zero degrees of freedom?