Final answer:
Strontium (Sr) with a mass number of 83 has 38 protons, 38 electrons, and 45 neutrons, as the mass number is the sum of protons and neutrons.
Step-by-step explanation:
The atomic number of strontium (Sr) is 38, which means it has 38 protons. The number of electrons in a neutral atom is the same as the number of protons, so a neutral atom of strontium also has 38 electrons. When given a mass number, such as 'strontium with a mass of 83', we are likely referring to an isotope of strontium, and the mass number represents the total number of protons and neutrons in the nucleus.
To find the number of neutrons, we subtract the atomic number (number of protons) from the mass number: neutrons = 83 - 38 = 45. Hence, for this isotope of strontium, there would be 38 protons, 38 electrons, and 45 neutrons.