The present system of atomic masses is based on _________ as the standard.

Correct option is C

The correct option is (C) Carbon-12.

Explanation:
The present system of atomic masses is based on the isotope Carbon-12 (C-12) as the standard. The atomic mass scale is defined such that the atomic mass of Carbon-12 is exactly 12 atomic mass units (amu), and the masses of other elements are compared relative to this standard.

Information Booster:

• The choice of Carbon-12 as the standard was made because it is abundant, stable, and easily accessible.

• Carbon-12 has exactly 6 protons and 6 neutrons, making it a convenient reference for defining atomic mass.

• The atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes, expressed relative to the mass of Carbon-12.

• This system of atomic masses is used in all scientific and industrial applications, including chemistry, physics, and medicine.