Answer:
The correct answer is - 97.
Explanation:
The mass number of an atom of an element is the total number of protons and neutrons present in an atom. Atoms normally have a different mass number but can be the same for different elements.
In the given case, there are 55 neutrons and 42 protons in an atom then the mass number of this atom would be:
mass number: 55+42
= 97.
