A slurry containing abrasive grains and a liquid medium, in which the abrasive grains contain at least one metal compound selected from the group consisting of a metal oxide and a metal hydroxide, the metal compound contains a metal capable of taking a plurality of valences, and when the slurry is brought into contact with a surface to be polished to bring the abrasive grains into contact with the surface to be polished, the slurry yields 0.13 or more in X-ray photoelectron spectroscopy as a ratio of the lowest valence among the plurality of valences of the metal.