The kelvin used to be tied to the triple point of water. What is it tied to now?
The Boltzmann constant✓الإجابة الصحيحة
The freezing and boiling points of water
The Planck constant
The average temperature of deep space
الشرح
The kelvin is fixed by giving the Boltzmann constant the exact value 1.380 649 × 10⁻²³ when expressed in joules per kelvin. The triple point of water has become a quantity that must be measured, rather than a defined value.