Question

What do you mean by triple point ?
Why the triple point of water is considered as a standard
fixed point in thermometry?​

Answer 1

Answer:

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.

Answer 2

Answer:

Triple point :

It is particular point in the phase diagram , representing  a particular pressure and temperature at which a substance can coexist in all phases i.e. solid , liquid and gas.

Triple point of water considered as a standard fixed point in thermometry and because it is fixed and occurs only for particular values of pressure which is equal to 0.46 cm of Hg and temperature equal to - 273.16 K.