Which of the following best describes the relationship between protons and neutrons in an element?

The statement that protons and neutrons can vary depending on the isotope accurately reflects the nature of atomic structure. Isotopes of an element have the same number of protons, which defines the element, but they differ in the number of neutrons. This variation in neutron count affects the atomic mass of the element but does not alter its chemical identity.

For example, carbon has isotopes such as carbon-12, which has six protons and six neutrons, and carbon-14, which has six protons and eight neutrons. This demonstrates how the relationship between protons and neutrons is not fixed and can vary across different isotopes, making option B the correct choice.

The other options do not accurately characterize the relationship: protons and neutrons are not always equal, protons are not larger than neutrons (in fact, they are similar in size), and neutrons certainly do exist as essential components of atomic nuclei.