Answer :
Final answer:
The question pertains to a specific isotope of thorium that has 90 protons and 137 neutrons. The atomic mass number of this isotope, calculated by combining the numbers of protons and neutrons, is 227. Thus, this isotope is referred to as Thorium-227.
Explanation:
The subject of this question is an isotope of thorium. An isotope is a variant of a particular chemical element, which differs in neutron number. In this case, the isotope of thorium in question has 90 protons and 137 neutrons. This information allows us to determine the isotope's atomic mass number, which is the sum of protons and neutrons in a nucleus. Thus, for this isotope of thorium, the atomic mass number would be 90 (protons) + 137 (neutrons) = 227. Therefore, this isotope is called Thorium-227.
Learn more about Isotopes here:
https://brainly.com/question/27475737
#SPJ3
