Slurry and polishing method

A slurry comprising abrasive grains and a liquid medium, wherein

• the abrasive grains include first particles and second particles in contact with the first particles,
• the second particles contain at least one metal compound selected from the group consisting of a metal oxide and a metal hydroxide,
• the at least one the metal compound contains a metal capable of taking a plurality of valences,
• a ratio of an atomic amount of the metal having the lowest valence of the plurality of valences to a total atomic amount of the metal is 0.10 or more in X-ray photoelectron spectroscopy, and
• an average particle size of the abrasive grains is 16 to 1050 nm.