Consider a solution made by mixing 500.0 mL of 0.04182 M Na2HAsO4 with 500.0 mL of 0.03645 M NaOH. Complete the mass balance expressions below for Na and arsenate species in the final solution.

Question

There are 4 arsenate species, but I only got three of them. I am unsure of what the last one could be.
The ones I have are HAsO4^2-, H3AsO4, AsO4^3-. I thought the last one would be H2AsO4^- but it wasn't correct.

Answer 1

Na2HAsO4
neutral compound

Answer 2

What about H2AsO4^-