Step-by-step explanation:
By definition the atomic number of an atom or element is the number of protons, while the mass number is equal to the number of protons plus the neutrons.
atomic number = n° of protons
mass number = n° of protons + n° of neutrons
We have to identify the number of protons and the number of neutrons in iodine-127. If we look for the atomic number in the periodic table we will see that the atomic number of iodine is 53. And the mass number is the one that we are given: 127.
We can use both values to get the number of protons and neutrons
atomic number = 53 = n° of protons
n° of protons = 53
mass number = 127 = n° of protons + n° of neutrons
n° of neutrons = mass number - n° of protons
n° of neutrons = 127 - 53
n° of neutrons = 74
Answer: 53 protons and 74 neutrons