In a nuclear reactor, the function of the moderator is to decrease

The $Q$ value of a nuclear reaction $\mathrm{A}+\mathrm{b}\to \mathrm{C}+\mathrm{d}$ is defined by $\mathrm{Q}=\left[{\mathrm{m}}_{\mathrm{A}}+{\mathrm{m}}_{\mathrm{b}}-{\mathrm{m}}_{\mathrm{C}}-{\mathrm{m}}_{\mathrm{d}}\right]{\mathrm{c}}^2$ where the masses refer to the respective nuclei. Determine from the given data the $Q$-value of the following reaction and state whether the reactions are exothermic or endothermic.

${}_6{}^{12}\mathrm{C}+{}_6{}^{12}\mathrm{C}\to {}_{10}{}^{20}\mathrm{N}\mathrm{e}+{}_2{}^4\mathrm{H}\mathrm{e}$
Atomic masses are given to be
$\mathrm{m}\left({}_2{}^4\mathrm{He}\right)=4.002603 \mathrm{u}$
$\mathrm{m}\left({}_6{}^{12}\mathrm{C}\right)=12.000000 \mathrm{u}$
$\mathrm{m}\left({}_{10}{}^{20}\mathrm{N}\mathrm{e}\right)=19.992439 \mathrm{u}$

The atoms which have the same mass number but different atomic numbers are called

Which is true about the isobars ?