How many donor groups (donor atoms) are present in diethylene triamine?

Which among the following statements is wrong regarding Mohr's salt?

An aqueous solution of the complex $[Cu(NH_3)_4]SO_4$ gives the test for:

Identify a ligand having two donor atoms but uses a pair of electrons of either donor atom to form a coordinate bond.

In the complex $K[Cr(H_2O)_2(C_2O_4)_2] \cdot 3H_2O$,the oxidation state and coordination number of the central metal ion are . . . . . . and . . . . . . respectively.

Which of the following is an example of a hexadentate ligand?