Isotopes

Atomic masses of isotopes of carbon (${}_6{}^{12}\mathrm{C}$) having neutrons 7 and 8 respectively are: 

There are _____ isotopes of Carbon.

Carbon has three isotopes with atomic mass number

Carbon has three isotopes.

Give examples of isotopes of carbon.

Define isotopes.

Give reasons.

 Isotopes of an element have the same atomic numbers.

Isotopes find important applications in a variety of areas in the fields of medicine, agriculture, generation of cheaper electricity, industry, radiocarbon dating, etc.
Which isotope is used for finding the age of a fossil?

A : ${}_6{}^{14}\mathrm{C}$

B : Uranium-$235$

C : ${}_{53}{}^{123}\mathrm{I}$

Enter your answer as A, B or C.