Consider the following atoms in which X represents the chemical symbol of the element: (4.4, 4.5) ¹⁶₈X ¹⁶₉X ¹⁸₁₀X ¹⁷₈X ¹⁸₈X a. What atoms have the same number of protons?

The atomic number of an element is the number of protons found in the nucleus of its atoms. It uniquely identifies an element and determines its position on the periodic table. In the context of isotopes, atoms with the same atomic number belong to the same element, regardless of their mass number.

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons, resulting in different mass numbers. For example, the isotopes of element X in the question share the same atomic number but differ in their mass numbers, indicating variations in their neutron count.

The mass number of an atom is the total number of protons and neutrons in its nucleus. It is represented as the superscript in the notation of an isotope (e.g., ¹⁶₈X). Understanding mass number is crucial for distinguishing between different isotopes of the same element, as it reflects the total nuclear composition.