Why is carbon-12 used as a standard for atomic-mass measurements?

Carbon-12 is used as the international standard for atomic mass measurements because it is the most abundant naturally occurring isotope of carbon, comprising approximately 98.93 percent of natural carbon.12

By scientific convention, the carbon-12 atom is assigned an atomic mass of exactly 12 units. Consequently, one atomic mass unit (amu)—also known as a dalton—is defined as exactly one-twelfth of the mass of a single carbon-12 atom. This provides a precise, stable reference point for expressing the masses of all other atoms, molecules, and nuclear particles.34