In an experiment, a student is given three different atoms labeled X, Y, and Z. Atom X has 11 protons, Y has 12 protons, and Z has 11 protons but different numbers of neutrons. The student is asked to identify what determines the identity of an element. Which statement correctly defines atomic number in this context?

A neutral atom of an element contains 17 protons and 17 electrons. Another atom of the same element is found in an ionized state with 17 protons but 18 electrons. The student is asked what remains unchanged in both cases.

During a class discussion, a teacher explains that all atoms of chlorine must have 17 protons, even if their masses differ due to neutrons. Students are asked why chlorine is always identified as chlorine.

A scientist studies three atoms of different elements. Atom A has atomic number 8, Atom B has atomic number 8 but is negatively charged, and Atom C has atomic number 9. The scientist concludes that:

In a nuclear physics model, students observe that when the number of protons in a nucleus increases from 6 to 7, the element completely changes from carbon to nitrogen. This observation proves that:

A student reads that isotopes of an element have the same atomic number but different mass numbers. The student is confused and asked to identify the correct reason.

An element is represented as (11 23 Na). A student is asked what the lower number (11) represents in this nuclear notation.

In a periodic table, elements are arranged in increasing order of atomic number. A student is asked why this arrangement is important for classification.

A researcher states: “If two atoms have the same number of protons but different masses, they still belong to the same element.” Students are asked to identify the correct justification.

In a high-energy experiment, a hydrogen atom loses its only electron and becomes a proton. Students are asked what changes and what remains constant in this transformation.