Respuesta :
Answer: Gallium-72
Explanation:
Atomic number is defined as the number of protons or number of electrons that are present in an atom. It is characteristic of an element.
Atomic number = Number of electrons = Number of protons = 31
Thus the element with atomic number of 31 is Gallium.
Mass number is defined as the sum of number of protons and neutrons that are present in an atom.
Mass number = Number of protons + Number of neutrons
There were 39 neutrons and then 2 more were added , thus there are 39+2 = 41 neutrons
Thus mass number = 31 + 41 = 72
Thus the element will be gallium with 72 mass number.