The question states which age group had the highest representation in India`s population according to the 1991 Census. To answer this, let`s examine each option:

Option 1: `60 years and above` refers to the elderly population. In most countries, including India, the percentage of elderly is usually lower compared to other age groups due to natural life expectancy.

Option 2: `35 to 55 years` is generally considered the working-age group. In 1991, this group represented the highest percentage of India`s population as people fell in this category were adults but were not old enough to be considered elderly.

Option 3: `25 to 34 years` represents young adults who are typically early in their careers. While a large number, they were not the largest demographic group in 1991.

Option 4: `5 to 14 years` includes young children and early adolescents. Despite high birth rates, they were not the largest population group.

Therefore, the correct answer is option 2, `35 to 55 years`, as this was the largest demographic in the 1991 Indian Census.