Negative 2 charges

• Hydrogen phosphate?

  HPO4^2-
• Oxalate?

  C2O4^2-
• Sulfite?

  SO3^2-
• Sulfate?

  SO4^2-
• Carbonate?

  CO3^2-
• chromate?

  CrO4^2-
• Dichromate?

  Cr2O7^2-
• Silicate?

  SiO3^2-
• Peroxide?

  O2^2-
• ide endings are nonmetals