Under the present definition, what is the status of the old metal cylinder, the international prototype of the kilogram?
Its mass is still exactly 1 kg by definition
Its mass now has to be measured by experiment, like that of any other object✓Правильный ответ
It was destroyed when the new definition took effect
It now defines the gram instead of the kilogram
Объяснение
The old definition fixed the prototype at exactly one kilogram and left the Planck constant to be measured. The new definition swaps the two around: the constant is now exact, and the cylinder is simply an object whose mass must be determined.