The triple point of water is a standard fixed point in the modern thermometry, why? What is wrong in taking the melting point of ice and boiling point of water as standard fixed point?

Explanation

To answer the question regarding why the triple point of water is a standard fixed point in modern thermometry and what is wrong with taking the melting point of ice and boiling point of water as standard fixed points, we can break down the solution into the following steps:

### Step-by-Step Solution:

1. **Definition of the Triple Point**:
The triple point of a substance is defined as the unique temperature and pressure at which all three phases (solid, liquid, and gas) coexist in thermodynamic equilibrium. For water, this occurs at a specific temperature of 0.01°C and a pressure of 611.657 pascals.

2. **Uniqueness of the Triple Point**:
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