Final answer:
The headlines regarding the discovery of element 100, comparing subatomic particle masses, and isotopes' similarities and differences would be questioned due to previously acquired knowledge in high school chemistry, such as the established characteristics of fermium, known mass comparisons of subatomic particles, and the defining traits of isotopes.
Step-by-step explanation:
The headlines a student who has just finished a high school chemistry course might question can be discussed in depth. Firstly, 'Chemists announce the discovery of element number 100' would raise questions because element 100, fermium, was already discovered in the 1950s, making this headline outdated. Secondly, 'Compare the masses of protons, neutrons, and electrons', suggests a comparison that is well-established: protons and neutrons have similar masses, which are much greater than the mass of an electron. Lastly, the question 'How are isotopes the same and how are they different?' relates to isotopes having the same number of protons (and hence the same chemical properties) but differing in the number of neutrons, affecting their mass number.
Addressing the other related topics, the atomic number is crucial because it defines the identity of an atom by indicating the number of protons in its nucleus. The number of protons and electrons in an atom are equal in a neutral atom, ensuring that the atom has no overall electric charge. Isotopes differ from each other in their number of neutrons, which results in different mass numbers, although they are the same element since they have the same atomic number. The mass number of an element is the sum of the protons and neutrons in the nucleus of an atom.