Final answer:
A neutral helium atom contains 2 protons and 2 electrons to maintain neutrality. Its mass number is 4, with 2 protons and 2 neutrons. Isotopes of helium may have different numbers of neutrons, resulting in various mass numbers.
Step-by-step explanation:
A neutral atom of helium has 2 protons and 2 electrons. This is because a neutral atom must have an equal number of protons and electrons. In the case of helium, the atomic number, which is the number of protons, is 2. Hence, to maintain neutrality, the number of electrons must also be 2.
The helium atom has a mass number of 4, calculated by adding the number of protons (2) and the number of neutrons (2). For isotopes of helium, the number of neutrons can vary, leading to different mass numbers.
The nuclear symbol for an atom of helium-4 is represented as:
4
He
2.