The Kol Rebellion was a significant uprising that occurred during 1831–32, primarily involving the Kol tribes in India. To determine which plateau region was mainly affected, let's analyze the options provided:

1. Deccan Plateau: This plateau region covers vast parts of southern and central India but it was not the primary area affected by the Kol Rebellion.
2. Chotanagpur Plateau: This plateau is located in eastern India, covering parts of Jharkhand, Bihar, Odisha, and West Bengal. The rebellion primarily emanated from this region as it was home to the Kol tribes.
3. Meghalaya Plateau: This plateau is further northeast, in the state of Meghalaya, and not the focal point of the Kol Rebellion.
4. Malwa Plateau: Located in central India, particularly in the state of Madhya Pradesh, this region was not significantly involved in the Kol Rebellion.

Based on the geographic and historical context, the Chotanagpur Plateau is the correct answer. The Kol Rebellion was driven by the discontent of the tribal population against revenue demands, feudalism, and exploitation at the hands of British authorities and moneylenders in this region. The tribals of Chotanagpur rose in revolt under leaders like Buddhu Bhagat and Joa Bhagat, marking this area as the epicenter of the movement.

Hence, the Kol Rebellion (1831–32) mainly affected the Chotanagpur Plateau.