The atmospheres of gas giants in the solar system are enriched with alkali metals which exist at different physical states under different pressure and temperature conditions. They affect the optical property of the deep atmosphere, how the internal heat is transported through the atmosphere and the microwave emission at long wavelengths. The 600 MHz MWR channel onboard the Juno orbiter found anomalous limb darkening at all latitudes. In previous laboratory studies, the opacities of NH3 and H2O in the microwave transmission have been measured extensively, and extrapolated to temperature and pressure relevant to 600 MHz at Jupiter. In this study, we investigate the condensation properties of alkali metals and their ionization in the deep atmosphere. We compute the microwave opacities and the respective weighting functions due to alkali metals. Using Juno MWR observations, and combining the impact of the alkali metals with the microwave properties of water and ammonia, we find that the abundances of alkali metals must be severely subsolar.