The solar interior has been scrutinized
by two different and independent probes during the last twenty years with important
revisions of the solar model,
including a recent heavy element abundance
revision. Today, we get a quantitatively coherent picture (even incomplete) of the solar (stellar) radiative zones.
In this review, we recall
the clues for solar gravitational settling definitively established by the seismic
determination of the photospheric helium content.
We comment also on the need for mixing in the transition region between radiation and convection
in the case of the Sun and of population II stars. We finally list the open questions and the importance to continue
more precise investigations of the solar (stellar) radiative zone in detecting gravity modes with the project DynaMICS.