Question

Which element has lowest number isotopes ?

• A. Hydrogen
• B. Oxygen
• C. Iron
• D. Carbon

Answer 1

The correct option is A

Hydrogen

The explanation for the correct answer

Isotopes are the variations of elements with the same atomic number but different mass numbers.

Option A

• Hydrogen ($\mathrm{H}$) has 3 isotopes.
• Which are Protium (${}_1{}^1\mathrm{H}$),Deuterium(${}_1{}^2\mathrm{H}$),Tritium(${}_1{}^3\mathrm{H}$).
• Each of these isotopes contains the same number of protons but a different number of neutrons.

Option B

• Oxygen($\mathrm{O}$) has 4 isotopes.
• Which include ${}_8{}^{15}\mathrm{O},{}_8{}^{16}\mathrm{O},{}_8{}^{17}\mathrm{O},{}_8{}^{18}\mathrm{O}$
• Each of these isotopes contains the same number of protons but a different number of neutrons.

Option C

• Iron($\mathrm{Fe}$) has 4 stable isotopes.
• Which Include ${}_{26}{}^{54}\mathrm{Fe},{}_{26}{}^{56}\mathrm{Fe},{}_{26}{}^{57}\mathrm{Fe},{}_{26}{}^{58}\mathrm{Fe}$
• Each of these isotopes contains the same number of protons but a different number of neutrons.

Option D

• Carbon($\mathrm{C}$) has 15 known isotopes${}_6{}^8\mathrm{C}\mathrm{to}{}_6{}^{22}\mathrm{C}$.
• But only ${}_6{}^{12}\mathrm{C},{}_6{}^{13}\mathrm{C},{}_6{}^{14}\mathrm{C}$ are stable.
• Each of these contains the same number of protons but a different number of neutrons.

Conclusion: Hence Option A is correct.