Which of the following pairs represent isotopes?

Question

Examoogle · Accepted Answer

The correct answer is Option B: Oxygen-16 and Oxygen-18. Isotopes are atoms of the same chemical element that have the same number of protons but a different number of neutrons in their nuclei. Consequently, they share the same atomic number but possess different mass numbers.

Step-by-Step Solution & Concepts:
Isotopes are atoms of the same chemical element that have the same number of protons but a different number of neutrons in their nuclei. Consequently, they share the same atomic number but possess different mass numbers.

Working Principle: The chemical identity of an element is determined exclusively by the number of protons (atomic number $Z$). Because isotopes contain identical proton counts, they exhibit near-identical chemical properties. The variation in mass is due solely to the difference in the number of neutrons ($N$), where the mass number $A = Z + N$.

Key Formulas: $A = Z + N$ — where $A$ is mass number, $Z$ is atomic number, and $N$ is neutron count

Key Points: Isotopes of an element have the same number of electrons, leading to identical chemical behavior.; The physical properties, such as density and boiling point, may vary slightly due to the different atomic masses.; Hydrogen has three naturally occurring isotopes: Protium ($^1H$), Deuterium ($^2H$), and Tritium ($^3H$).

Advantages: Used in medical imaging and radiotherapy.; Enables radioactive dating (e.g., Carbon-14 dating) to determine the age of organic materials.

Disadvantages: Radioactive isotopes can be harmful if not handled with specialized equipment and shielding.; Radioactive waste requires long-term, complex storage solutions.

Applications: Uranium-235 is used as fuel in nuclear power reactors.; Iodine-131 is used for treating thyroid disorders.

Additional Info: Oxygen-16 ($Z=8, A=16$) and Oxygen-18 ($Z=8, A=18$) both have 8 protons.. Option A: Carbon ($Z=6$) and Nitrogen ($Z=7$) are different elements.. Option C: Sodium ($Z=11$) and Magnesium ($Z=12$) are different elements.. Option D: Hydrogen ($Z=1$) and Helium ($Z=2$) are different elements.

Answer: B is correct — Oxygen-16 and Oxygen-18 are isotopes because they have the same atomic number (8) but different mass numbers.

Exam Tip: Always verify the atomic number ($Z$) first when identifying isotopes; if the elements are different, they cannot be isotopes.

Examoogle · Answer

Option A: Carbon-12 and Nitrogen-14

Examoogle · Answer

Option C: Sodium-23 and Magnesium-24

Examoogle · Answer

Option D: Hydrogen-1 and Helium-4

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