Question

According to the periodic table, carbon has an atomic mass of 12.011 u. This indicates that the most abundant isotope of carbon is
carbon-11.
carbon-12.
carbon-13.
carbon-14.

Answer 1

Carbon 12 is the most available carbon form in nature.

Answer 2

The most abundant of all of the isotopes of an element will be the one who's mass the mass of element is closest to. In this case, the mass of atomic carbon is closest to the mass of carbon-12.
Thus, Carbon-12 is the most abundant isotope.