Explanation: Madhya Pradesh has the largest population of Scheduled Tribes in India. The state has a significant tribal population, and tribes such as the Bhils, Gonds, and Baigas are among the most prominent.
Other Options Explained:

(A) Himachal Pradesh → Although Himachal Pradesh has a tribal population, it is not the largest in the country.
(C) Arunachal Pradesh → Arunachal Pradesh has a high percentage of Scheduled Tribes, but the total population is smaller compared to Madhya Pradesh.
(D) Sikkim → Sikkim also has a significant tribal population, but again, it is not the largest in India.

Thus, the correct answer is (B) Madhya Pradesh.