Final answer:
The element with the atomic mass of 48.7 is Manganese (Mn), which has 24 neutrons in its nucleus.
Step-by-step explanation:
The element with the atomic mass of 48.7 is Manganese (Mn).
Manganese has an atomic number of 25, which means it has 25 protons. It also has a mass number of 48.7, which is the sum of the protons and neutrons in its nucleus. Therefore, the number of neutrons can be calculated by subtracting the atomic number from the mass number:
Number of neutrons = Mass number - Atomic number = 48.7 - 25 = 23.7
Since the number of neutrons must be a whole number, we round it to the nearest whole number, which gives us 24 neutrons in a manganese atom.