According to the 1991 census, the state/union territory with the highest percentage of scheduled castes population is Punjab. This means that out of all the states and union territories in India, Punjab had the highest proportion of people who belonged to the scheduled castes category. It is important to note that scheduled castes are historically disadvantaged social groups in India who have been traditionally subjected to social discrimination and injustice. Therefore, Punjab stood out in terms of having a larger population of scheduled castes compared to other states and union territories. This information provides insights into the distribution and representation of different social groups within the country.