Question

the number of protons defines an elemen
all atoms of the same element have the same

multiple choice

atomic number.

number of ions.

atomic mass.

number of neutrons.

number of electrons.

Explanation:

1. Recall the definition of atomic number: The atomic number of an element is equal to the number of protons in its nucleus.
2. Analyze each option:

• "atomic number": Since all atoms of the same element have the same number of protons, they have the same atomic number. This matches the concept.
• "number of ions": Ions are formed by gaining or losing electrons, and the number of ions isn't a characteristic defined by the element's protons. Different atoms of the same element can form different numbers of ions (or not form ions at all) depending on conditions.
• "atomic mass": Atomic mass depends on the sum of protons and neutrons. Isotopes of an element have the same number of protons but different numbers of neutrons, so their atomic masses differ.
• "number of neutrons": Isotopes of an element have different numbers of neutrons, so this is not the same for all atoms of the same element.
• "number of electrons": Atoms can gain or lose electrons to form ions, so the number of electrons can vary for atoms of the same element (e.g., a sodium atom and a sodium ion have different numbers of electrons).

Answer:

A. atomic number.