Final answer:
A neutral element with an atomic number of 18 and atomic mass of 40 has 18 protons, 22 neutrons, and 18 electrons.
Step-by-step explanation:
If a neutral element has an atomic number of 18 and an atomic mass of 40, we can determine the number of protons, neutrons, and electrons it has. The atomic number tells us that the element has 18 protons. Since the element is neutral, it must also have 18 electrons because the number of protons must equal the number of electrons to maintain neutrality. The atomic mass, which is 40 in this case, is the sum of protons and neutrons. Therefore, to find the number of neutrons, we subtract the number of protons from the atomic mass:
number of neutrons = atomic mass - atomic number
number of neutrons = 40 - 18 = 22
Thus, the element has 18 protons, 22 neutrons, and 18 electrons.