Question 129: Atoms & Nuclei

Question

Which of the following pair of nuclei are isobars of the element?

Accepted Answer

Atoms are represented by the notation $\mathrm{X}_{\mathrm{Z}}^{\mathrm{A}}$, where :
1. A is the Mass Number (total number of protons and neutrons).
2. $ \mathrm{Z}$ is the Atomic Number (number of protons).
Isobars are atoms of different chemical elements that have the same mass number (A) but different atomic numbers (Z).
Option A :
$\mathrm{H}_1^3$ and $\mathrm{He}_2^3$
Mass numbers: 3 and 3 (Same)
Atomic numbers: 1 and 2 (Different)
Since they have the same mass number ( $A=3$ ) but represent different elements ( $Z=1$ vs $Z=2$ ), they are Isobars. Hence, option (A) is correct.
Option B :
$\mathrm{Hg}_{80}^{198}$ and $\mathrm{Au}_{79}^{197}$
Mass numbers: 198 and 197 (Different)
Atomic numbers: 80 and 79 (Different)
So, $\mathrm{Hg}_{80}^{198}$ and $\mathrm{Au}_{79}^{197}$ are neither isobars nor isotopes. Hence, option (B) is incorrect.
Option C :
$\mathrm{H}_1^2$ and $\mathrm{H}_1^3$
Mass numbers: 2 and 3 (Different)
Atomic numbers: 1 and 1 (Same)
So, $\mathrm{H}_1^2$ and $\mathrm{H}_1^3$ are Isotopes of Hydrogen (Deuterium and Tritium). Hence, option (C) is incorrect.
Option D :
$\mathrm{U}_{92}^{236}$ and $\mathrm{U}_{92}^{238}$
Mass numbers: 236 and 238 (Different)
Atomic numbers: 92 and 92 (Same)
So, $\mathrm{U}_{92}^{236}$ and $\mathrm{U}_{92}^{238}$ are Isotopes (same element, different mass) not isobars. Hence, option (D) is incorrect.

Answer

${ }_1^3 \mathrm{H}$ and ${ }_2^3 \mathrm{He}$

Answer

${ }_{80}^{198} \mathrm{Hg}$ and ${ }_{79}^{197} \mathrm{Au}$

Answer

${ }_1^2 \mathrm{H}$ and ${ }_1^3 \mathrm{H}$

Answer

${ }_{92}^{236} \mathrm{U}$ and ${ }_{92}^{238} \mathrm{U}$

Atoms & Nuclei

Which of the following pair of nuclei are isobars of the element?

Choose the correct answer: