1. Identify the ligand shown

   The ligand referred to in such coordination-compound questions is typically judged by the number of donor atoms through which it can attach to a metal ion.

2. Recall the definition of denticity

   Denticity = number of donor atoms in a ligand that can simultaneously coordinate to the central metal atom.

   • Bidentate $\rightarrow 2$ donor atoms
   • Tridentate $\rightarrow 3$ donor atoms
   • Tetradentate $\rightarrow 4$ donor atoms
   • Hexadentate $\rightarrow 6$ donor atoms

3. Count the donor sites in the given ligand

   The given ligand has 4 coordinating donor atoms, so it can bind through four sites to the metal ion.

4. Conclusion

   Therefore, the ligand is tetradentate.

5. Option check

   • A: hexadentate $\rightarrow$ incorrect
   • B: bidentate $\rightarrow$ incorrect
   • C: tetradentate $\rightarrow$ correct
   • D: tridentate $\rightarrow$ incorrect

Hence, the correct answer is C.