  Motivated by the solar composition problem and by using the recently
developed Linear Solar Model approach, we analyze the role of opacity and
metals in the sun. After a brief discussion of the relation between the effects
produced by a variation of composition and those produced by a modification of
the radiative opacity, we calculate numerically the opacity kernels that, in a
linear approximation, relate an arbitrary opacity variation to the
corresponding modification of the solar observable properties. We use these
opacity kernels to discuss the present constraints on opacity (and composition)
provided by helioseismic and solar neutrino data.
