Question

What is the mass number of an istope of this atom that has 2 neutrons

Answer 1

A=mass number
Z=atomic number
N=number of neutrons.

A=Z+N

The only one isotope of an atom with 2 neutrons is Tritium, it is an isotope of Hydrogen with 2 neutrons.

Therefore:
N=2
Z(H)=1

A=Z+N
A=1+2=3

Answer: The mass number would be 3 (A=3), and it would be an isotope of Hydrogen named Tritium.

Answer 2

The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13 and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively