Substances with same atomic number but different mass number are
**Core Concept**
Isotopes are atoms of the same chemical element that have the same atomic number (i.e., the same number of protons in their atomic nuclei) but differ in neutron number and, consequently, mass number. This results in atoms of the same element with different physical properties.
**Why the Correct Answer is Right**
Isotopes have the same atomic number because they have the same number of protons in their atomic nuclei. However, they differ in mass number due to the varying number of neutrons in their atomic nuclei. For example, carbon-12 and carbon-14 are isotopes of carbon, with atomic numbers 6 and mass numbers 12 and 14, respectively. The presence of additional neutrons in carbon-14 results in a higher mass number compared to carbon-12.
**Why Each Wrong Option is Incorrect**
**Option A:** Not applicable (no information provided).
**Option B:** Not applicable (no information provided).
**Option C:** Not applicable (no information provided).
**Option D:** Not applicable (no information provided).
**Clinical Pearl / High-Yield Fact**
Isotopes with different mass numbers exhibit distinct physical properties, such as varying half-lives, which can impact their biological and chemical behavior. This knowledge is essential in understanding radiopharmaceuticals and their applications in nuclear medicine.
**Correct Answer:** C. Isotopes.