Which of the following is not an isotope of hydrogen? — Hydrogen Chemistry Question

💡 Solution & Explanation

# Identifying Non-Isotopes of Hydrogen **Understanding Isotopes:** Isotopes are atoms of the same element (same atomic number $Z$) with different numbers of neutrons (different mass number $A$). **Hydrogen's Isotopes:** All hydrogen isotopes have $Z = 1$ (one proton): - **Protium ($^1H$):** 1 proton, 0 neutrons - **Deuterium ($^2H$ or D):** 1 proton, 1 neutron - **Tritium ($^3H$ or T):** 1 proton, 2 neutrons **Why B is Correct:** Option B must contain an atom with $Z \neq 1$ (different atomic number than hydrogen). This could be: - Helium ($^4He$, $Z = 2$) - Any other element Since isotopes *must* have the same atomic number, any element other than hydrogen is **not an isotope of hydrogen** — it's a different element entirely. **Answer:** B is correct because it represents an atom with a different atomic number, making it a different element rather than an isotope of hydrogen.