  We study the equation of state, fluctuations and static correlators of
electric charge, baryon number and strangeness, by considering a realization of
the Hadron Resonance Gas model in the light flavor sector of QCD. We emphasize
the importance of these observables to study, within this approach, the
possible existence of exotic and missing states in the hadron spectrum. Some
preliminary results for the baryon spectrum have been obtained within a
relativistic quark-diquark model, leading to an overall good agreement with the
spectrum obtained with other quark models. Finally, it is conjectured, within
the Hadron Resonance Gas approach, the existence of a singularity in the
correlators at zero temperature, which turns out to be analogous to the
divergence of the partition function at the Hagedorn temperature.
