A student obtains the following schematic photoelectron spectra for \(3\) gaseous, isoelectronic samples labeled \(P\), \(Q\), and \(R\). The samples, in unknown order, are \(\text{Ne(g)}\), \(\text{Na}^{+}\text{(g)}\), and \(\text{Mg}^{2+}\text{(g)}\). All spectra are plotted on the same relative binding-energy scale.

Which statement correctly identifies the sample whose \(2p\) electrons experience the greatest effective nuclear charge and explains the evidence from the spectra?