Arsenate
Arsenate' is an ion. Arsenates are salts of arsenic acid. They are oxidizing agents. Sometimes, not all of the protons are taken away from the arsenic acid and then hydrogen arsenate salts are formed. Arsenate can replace phosphate in the cells but it does not work like phosphate does. The cell dies, and that is why arsenates are toxic. Some bacteria can use arsenate instead of phosphate, though.