Explanation:

- Nepal:

- Correct Answer: Bada Dashain is the biggest festival in Nepal.

- It is a festival of Hindu origin, celebrated with great enthusiasm.

- The festival lasts for 15 days, marking a period of family gatherings, blessings, and worship.

- India:

- Although Dashain is celebrated by Nepali communities in India, it is not the biggest festival in the country.

- Festivals like Diwali and Holi overshadow it in terms of scale.

- Bangladesh:

- Predominantly celebrates Islamic festivals such as Eid.

- Hindu festivals do occur but on a smaller scale.

- Pakistan:

- Also mainly celebrates Islamic festivals.

- Hindu festivals are observed by minority communities.

- Myanmar:

- Celebrates various Buddhist festivals.

- Hindu festivals are not widely celebrated.