Which Constitutional Amendment Act substituted the 1991 census with the 2001 census as the basis for the delimitation of electoral constituencies in India?

Explanation

The 87th Constitutional Amendment Act of 2003 altered the census year basis for the delimitation of electoral constituencies from 1991 to the 2001 census. On the other hand, the 89th Constitutional Amendment Act is related to the creation of separate National Commissions for Scheduled Castes (Article 338) and Scheduled Tribes (Article 338A).