Question

How many molecules of ethylene diamine will react with?

Answer 1

Ethylene diamine is a bidentate ligand, so the answer is probably 2 or 3, since it will be difficult to displace the last two water molecules, which usually fill the polar positions.. 

The co-ordination sphere of Ni(II) is a square bipyrimid, with a ligand at each vertex, for a total of 6.