What are carbon-12, carbon-13, and carbon-14?
a. atoms with different number of electrons
b. different elements
c. different isotopes of the same element

C. different isotopes of the same element

Explanation:

Isotopes are the atoms of same element having different number of neutrons. The number of protons is same in all the isotopes which means that all the atoms have same atomic number. Having different number of neutrons, these  atoms have different mass number but same atomic number.

Carbon-12, Carbon-13, and Carbon-14 have same atomic number - 6 but different mass number i.e have different number of neutrons.

Carbon-12 has 6 neutrons, carbon-13 has 7 neutrons and carbon 14 has 8 neutrons. These are different isotopes of the same element.