Humber Admissions Practice Test

Which characteristic is common to all atoms of a specific element?

1. Number of neutrons

2. Number of protons

3. Mass number

4. Charge

The correct answer is: Number of protons

The characteristic that is common to all atoms of a specific element is the number of protons. Each element on the periodic table is defined by its atomic number, which is the number of protons present in the nucleus of its atoms. For example, all carbon atoms have six protons, which is what distinguishes carbon from other elements. This specific number of protons sets the chemical properties and behavior of the element, thereby establishing its identity. While the number of neutrons can vary among isotopes of an element, the number of protons remains constant for all atoms of that element. The mass number, which represents the total number of protons and neutrons in an atom, can change depending on the isotopes, so it is not a defining characteristic. Charge, in general, pertains to the balance between protons and electrons, but this does not define the element itself. Therefore, it is the number of protons that serves as the key identifier for the atoms of any specific element.