Question 19

Protons can always be used to identify an atom.

Protons are the defining subatomic particles of an atom, as the number of protons in an atom's nucleus determines its atomic number and, consequently, its identity as a particular element.

A) Protons

Protons are the fundamental particles that define the identity of an atom. Each element on the periodic table is distinguished by its number of protons; for example, hydrogen has one proton, while carbon has six. This unique count of protons allows for the identification of an atom as a specific element.

B) Neutrons

Neutrons do not determine the identity of an atom; rather, they contribute to the mass and stability of the nucleus. While isotopes of an element differ in the number of neutrons, the elemental identity is still defined by the number of protons. Thus, neutrons cannot be used to identify an atom.

C) Electrons

Electrons are involved in chemical bonding and reactions, but they do not determine the identity of an atom. The number of electrons can change in ions or during chemical reactions, making them unreliable for identifying the element, unlike protons.

D) None of the above

This option suggests that no subatomic particle can identify an atom, which is incorrect. Protons serve as the definitive identifier for each element. Therefore, this choice does not hold true.

Conclusion

Protons are essential for identifying atoms because they establish the atomic number, which corresponds to a specific element on the periodic table. In contrast, neutrons and electrons vary between isotopes and ions, respectively, making them unsuitable for elemental identification. Thus, the only reliable subatomic particle for this purpose is protons.