The symbols represent four atoms. The letters used are not the usual atomic symbols. Which atoms are isotopes of the same element?

2.3.1. Define isotopes as different atoms of the same element that have the same number of protons but different numbers of neutrons

2.3.2. Interpret and use symbols for atoms, $\text { e.g. }{ }_{6}^{12} \mathrm{C} \text {, and ions, e.g. }{ }_{17}^{35} \mathrm{Cl}$

2.3.3. State that isotopes of the same element have the same chemical properties because they have the same number of electrons and therefore the same electronic configuration

2.3.4. Calculate the relative atomic mass of an element from the relative masses and abundances of its isotopes