If we remove one neutron from an atom, the mass number and atomic number will remain unchanged. The mass number of an atom is equal to the sum of its protons and neutrons, while the atomic number is equal to the number of protons.
When we remove a neutron from an atom, we are altering its isotopic composition. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. By removing a neutron, we are essentially changing the specific isotope of the element.
Since the mass number is the sum of protons and neutrons, removing one neutron will decrease the mass of the atom by one. However, the atomic number, which represents the number of protons, remains the same because we have not altered the number of protons in the nucleus.
For example, let's consider the element carbon. Carbon has an atomic number of 6, meaning it has 6 protons. It also has several isotopes, including carbon-12, carbon-13, and carbon-14. The numbers 12, 13, and 14 refer to the respective mass numbers of these isotopes, which indicate the total number of protons and neutrons in their nuclei.
If we remove one neutron from a carbon-13 atom, we are left with a carbon-12 atom. The mass number decreases from 13 to 12, but the atomic number remains 6 because the number of protons hasn't changed.
In summary, removing one neutron from an atom changes its isotopic composition and decreases the mass number but does not affect the atomic number since it represents the number of protons in the nucleus.