Final answer:
The atomic mass of carbon at 12.011 represents the average mass of all carbon isotopes, indicating that carbon is a mixture of isotopes such as Carbon-12 and Carbon-13.
Step-by-step explanation:
The atomic mass for the element carbon (C) is 12.011. This number represents the average mass of all carbon isotopes rather than the mass of an individual atom. This indicates that carbon is a mixture of isotopes because the atomic mass reflects the weighted average of the isotopes' masses based on their relative abundance. Carbon has several isotopes, but the most common are Carbon-12 and Carbon-13, with Carbon-12 being the most abundant.
Therefore, the correct answer to the question is B) It represents the average mass of all carbon isotopes.
Carbon-12 has 6 protons and 6 neutrons, giving it a mass number of 12 amu. In contrast, Carbon-13 has one additional neutron, hence its mass number is 13 amu. When these isotopes' mass numbers and their abundances are combined in a weighted average, we get the atomic mass of carbon as listed on the periodic table, which slightly exceeds 12 amu.