Buddha attained mahaparinirvana in the republic of Mallas.

The Mallas were an ancient republic in India and were known for their democratic governance. They were a confederacy of several clans, and their capital was Kushinagar, where Buddha attained mahaparinirvana.

Here are the reasons why the correct answer is option 'A':

1. Historical records: The Mahaparinibbana Sutta, one of the important texts in Buddhism, provides detailed accounts of Buddha's final days and his attainment of mahaparinirvana. According to this text, Buddha traveled to different places during his last journey, and finally arrived in Kushinagar, the capital of the Mallas republic, where he attained mahaparinirvana.

2. Archaeological evidence: Archaeological excavations in Kushinagar have unearthed several ancient structures and relics associated with Buddha's mahaparinirvana. These include the Mahaparinirvana Stupa, which is believed to enshrine the remains of Buddha, and the Ramabhar Stupa, which marks the site where Buddha was cremated.

3. Buddhist tradition: The Mallas were known for their reverence towards Buddha and played a significant role in his final moments. It is believed that the Mallas requested Buddha to stay in Kushinagar until his death, and they also organized a grand cremation ceremony after his mahaparinirvana.

4. Cultural significance: Kushinagar has been a major pilgrimage site for Buddhists for centuries, attracting devotees from all over the world. The Mallas' association with Buddha's mahaparinirvana has contributed to the cultural and religious significance of this place.

In conclusion, Buddha attained mahaparinirvana in the republic of Mallas, specifically in Kushinagar. This event holds immense importance in Buddhist history and has shaped the religious and cultural landscape of the region.