Question

The mass of a neutral carbon atom, a specimen of the most common isotope, in ground state is:

• A. equal to 12 u
• B. less than 12 u
• C. more than 12 u
• D. Depends on the allotrope, whether it is graphite, charcoal or diamond.

Answer 1

The correct option is A

equal to 12 u

The unified atomic mass unit, 'amu', is defined as '${\frac{1}{12}}^{th}$ of the mass of a neutral Carbon-12 in its lowest energy state which contains six protons, six neutrons and six electrons.' So, by definition, a Carbon-12 atom in ground state has a mass of exactly 12 amu.