The kilogram is now derived by fixing the value of which physical constant?
Answer
Planck constant ($h$)
Following the 2019 redefinition, the kilogram is now derived by fixing the value of the Planck constant ($h$).

Related Questions
What does the abbreviation "SI" in SI units stand for?How many independent base units form the foundation of the SI system?Which body formalizes and maintains the current structure of the SI system?In what year were the SI units officially redefined to be based on nature’s inherent constants?Prior to the 2019 redefinition, what physical object defined the standard for the kilogram?The kilogram is now derived by fixing the value of which physical constant?What specific phenomenon is the definition of the second (time) currently tied to?Which derived SI unit is equivalent to $\text{kg} \cdot \text{m}/\text{s}^2$ and represents force?What characteristic of SI prefixes ensures they prevent ambiguity in international documentation?What is the SI base unit symbol for Amount of Substance?