EDTA combines with cations to form which of the following species?

The correct answer is option 1. Chelates.

EDTA (ethylenediaminetetraacetic acid) is a chelating agent that combines with metal cations to form stable complexes known as chelates. 

Chelation involves the formation of a complex where the chelating agent (EDTA) binds to a metal ion at multiple points. EDTA is a hexadentate ligand, meaning it has six donor atoms (four carboxyl groups and two amine groups) that can coordinate to a single metal ion, forming a ring-like structure around the ion. When EDTA binds to a metal cation, it forms a stable complex called a chelate. This chelation process is highly stable because the multiple bonds formed between the metal and EDTA reduce the possibility of the metal ion being replaced or precipitated out of solution. These chelates are widely used in various applications, including water treatment, medicine (as a chelating agent to remove heavy metals from the body), and analytical chemistry (as a titrant in complexometric titrations).

Conclusion: EDTA combines with metal cations to form chelates. Therefore, the correct answer is: Chelates.