Introduction:
The Nirguna School of Bhakti is a spiritual tradition within Hinduism that focuses on the formless and attribute-less nature of God. It emphasizes the idea that God cannot be comprehended through human senses or limited by physical form or attributes. The followers of this school believe in the ultimate reality as formless and attribute-less, and they seek to attain union with the divine through intense devotion and love.

Explanation:
Among the given options, Chaitanya did not belong to the Nirguna School of Bhakti. Here is the explanation:

Kabir:
- Kabir was a 15th-century mystic poet and saint who is considered one of the most important figures in the Bhakti movement.
- He was a follower of the Nirguna School of Bhakti and emphasized the formless and attribute-less nature of God.
- Kabir's verses and teachings reflect the idea of transcending the physical and material world to attain union with the divine.

Nanak:
- Guru Nanak Dev, the founder of Sikhism, was a 15th-century saint and a prominent figure in the Bhakti movement.
- He also belonged to the Nirguna School of Bhakti and emphasized the formless and attribute-less nature of God.
- Nanak's teachings focused on the unity of God and the importance of selfless service and devotion.

Dadu:
- Dadu Dayal was a 16th-century poet and saint who belonged to the Nirguna School of Bhakti.
- He emphasized the formless and attribute-less nature of God and the importance of love and devotion in attaining union with the divine.
- Dadu's teachings emphasized the inner experience of God rather than external rituals and practices.

Chaitanya:
- Chaitanya Mahaprabhu was a 16th-century saint and the founder of the Gaudiya Vaishnavism tradition.
- Unlike the other three saints mentioned above, Chaitanya did not belong to the Nirguna School of Bhakti.
- He belonged to the Saguna School of Bhakti, which emphasizes devotion to a personal form of God, particularly the worship of Lord Krishna.
- Chaitanya's teachings focused on the path of bhakti (devotion) and the chanting of the holy names of God as a means to attain love and union with the divine.

Conclusion:
Chaitanya Mahaprabhu, among the given options, did not belong to the Nirguna School of Bhakti. While Kabir, Nanak, and Dadu were followers of the Nirguna School and emphasized the formless and attribute-less nature of God, Chaitanya belonged to the Saguna School and emphasized devotion to a personal form of God, particularly Lord Krishna.