NH2NH2, also known as hydrazine, can act as both a monodentate and a bridging ligand. Let's understand each concept in detail:

**Monodentate Ligand:**
A monodentate ligand is a ligand that can donate only one pair of electrons to form a coordinate bond with a metal ion. In the case of hydrazine (NH2NH2), it contains two nitrogen atoms, each with a lone pair of electrons that can be donated to a metal ion. Therefore, hydrazine can act as a monodentate ligand by donating one pair of electrons from one nitrogen atom to form a coordinate bond with a metal ion.

**Bridging Ligand:**
A bridging ligand is a ligand that can simultaneously donate a pair of electrons to two or more metal ions, thereby forming a bridge between them. In the case of hydrazine, it contains two nitrogen atoms, each with a lone pair of electrons. These lone pairs can simultaneously coordinate with two or more metal ions, bridging them together. Therefore, hydrazine can also act as a bridging ligand.

**Explanation of Correct Option (D):**
The correct answer is option (D) because hydrazine (NH2NH2) can act as both a monodentate and a bridging ligand. It can donate one pair of electrons from one nitrogen atom to form a coordinate bond with a metal ion, acting as a monodentate ligand. Additionally, it can also simultaneously coordinate with two or more metal ions, bridging them together, acting as a bridging ligand.

Therefore, option (D), which states that hydrazine can act as both a monodentate and a bridging ligand, is the correct answer.