The question asks us to identify the Bhakti saint who did not belong to the Nirguna School of Bhakti. To understand the answer, let`s first clarify what the Nirguna School of Bhakti is.

The Nirguna School of Bhakti is a belief system within Bhakti movement that emphasizes devotion to a formless, attributeless God. In this school, the focus is on the spiritual essence of God rather than any physical or tangible form.

Now let`s analyze each option:

Option 1: Kabir - Kabir was a prominent Bhakti saint who belonged to the Nirguna School of Bhakti. He advocated for the worship of a formless and transcendent God.

Option 2: Nanak - Nanak, the founder of Sikhism, also belonged to the Nirguna School of Bhakti. Sikhism teaches the worship of the formless divine entity.

Option 3: Dadu - Dadu, another significant Bhakti saint, also belonged to the Nirguna School of Bhakti. His teachings emphasized the importance of devotion to a formless God.

Option 4: Chaitanya - Chaitanya, on the other hand, did not belong to the Nirguna School of Bhakti