what three forms of ice are present at the triple point marked o
Triple point The single combination of pressure and temperature at which liquid water, solid ice, and water vapor can coexist in a stable equilibrium occurs at exactly 273.16 K (0.01 °C; 32.02 °F) and a partial vapor pressure of 611.657 pascals (6.11657 mbar; 0.00603659 atm).[4][5] At that point, it is possible to change all of the substance to ice, water, or vapor by making arbitrarily small changes in pressure and temperature. Even if the total pressure of a system is well above the triple point of water, provided that the partial pressure of the water vapor is 611.657 pascals, then the system can still be brought to the triple point of water. Strictly speaking, the surfaces separating the different phases should also be perfectly flat, to negate the effects of surface tension.
Freezing-point depression The freezing point is the temperature at which the vapor pressures of liquid solvent and solid solvent are equal. When a non-volatile solute is added to a volatile liquid solvent, the solution vapor pressure will be lower than that of the pure solvent. As a result the solid will reach equilibrium with the solution at a lower temperature than with the pure solvent.[1]