ANS:C - isotopes

Atoms of the same element but with different masses are called isotopes. Isotopes have the same number of protons (and hence the same atomic number) but different numbers of neutrons, resulting in different mass numbers. This variation in the number of neutrons accounts for the difference in mass among isotopes of the same element. Therefore, the correct term is isotopes. Isotopes are atoms of the same chemical element that have the same number of protons (and therefore the same atomic number) but different numbers of neutrons in their nuclei. This variation in the number of neutrons leads to differences in mass numbers for isotopes of the same element. Here's a breakdown of the concept:

1. Same Element: Isotopes belong to the same chemical element, which means they have the same number of protons in their atomic nuclei. The number of protons defines the element's identity. For example, all carbon atoms have 6 protons in their nuclei, making them carbon atoms.
2. Different Masses: While isotopes have the same number of protons, they can have different numbers of neutrons. Neutrons are electrically neutral particles found in the atomic nucleus along with protons. Since isotopes of the same element have different numbers of neutrons, they also have different masses. This difference in mass numbers results from the varying numbers of neutrons.
3. Naming Convention: Isotopes are often named based on their mass number, which is the sum of the number of protons and neutrons in the nucleus. For example, carbon-12 (12C) and carbon-14 (14C) are two isotopes of carbon. Carbon-12 has 6 protons and 6 neutrons, while carbon-14 has 6 protons and 8 neutrons.
4. Chemical Similarity: Isotopes of the same element exhibit similar chemical properties because they have the same number of protons and electrons. Chemical reactions primarily involve the interactions of electrons, and since isotopes of the same element have the same electron configurations, their chemical behavior is similar.
5. Variety and Occurrence: Many elements have multiple naturally occurring isotopes. For example, carbon has isotopes with mass numbers 12, 13, and 14, while hydrogen has isotopes with mass numbers 1, 2, and 3. Some elements may also have artificially created isotopes through nuclear reactions.
6. Applications: Isotopes have various practical applications, including radiometric dating (using isotopes with known decay rates to determine the age of materials), medical diagnostics and treatment (using radioactive isotopes in imaging and therapy), and isotopic labeling (using isotopes to track chemical reactions in scientific research).

In summary, isotopes are variants of the same element with different numbers of neutrons, resulting in differences in mass numbers. Despite these differences in mass, isotopes share similar chemical properties due to their identical numbers of protons and electrons.