Isotopes have identical chemical properties; physical properties can differ.

• A. Isotopes have different chemical properties
• B. Isotopes have different numbers of protons
• C. Isotopes have identical chemical properties; physical properties can differ
• D. Isotopes are different elements

Answer: (C)

The main idea here is that chemical properties are governed by electron configuration, not nuclear mass. Isotopes have the same number of protons and the same electrons, so they form bonds and participate in reactions in the same way. The differences between isotopes come from neutrons, which change the mass but not the electron cloud, so physical properties that depend on mass or vibrational energy—like density, melting/boiling points, and diffusion rates—can differ.

That’s why the statement that isotopes have identical chemical properties while their physical properties can differ is the best description. The other ideas would imply a change in the electron structure or identity: having a different number of protons would make a different element, and claiming different chemical properties would contradict how chemical reactivity is set by electrons.