Which of the following pairs is an isobar

${ }_1 H^1$ and ${ }_1 H^2$

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

${ }_6 C^{12}$ and ${ }_6 C^{13}$

${ }_{15} P^{30}$ and ${ }_{14} S^{30}$