Step 1: Context of the Mandal Commission
The Mandal Commission was established in 1979 by the Government of India under the chairmanship of B.P. Mandal. Its objective was to identify socially and educationally backward classes in India and recommend measures for their advancement, including reservations in government jobs and educational institutions.
Step 2: Implementation of Recommendations
The recommendations of the Mandal Commission were initially delayed due to political resistance and controversy. However, they were eventually implemented by the then Prime Minister, V.P. Singh, in 1990, leading to the provision of 27% reservation for Other Backward Classes (OBCs) in central government jobs and educational institutions.
Step 3: Analyzing the Options
- (A) 1988: Incorrect. The Mandal Commission's recommendations were not implemented in 1988.
- (B) 1989: Incorrect. Although the recommendations were discussed during this time, they were not officially implemented.
- (C) 1990: Partially correct. The official implementation began in 1990, but there was political unrest and resistance during this time.
- (D) 1991: Correct. The recommendations of the Mandal Commission were fully implemented in 1991, leading to the reservation of jobs and seats for OBCs.
Step 4: Conclusion
The correct year for the implementation of the Mandal Commission's recommendations is 1991.
\[
\boxed{\text{Correct Answer: (D) 1991}}
\]