The official religion of the state in India is None (option D). Let's delve into the details to understand why.

Historical Background:
- India is known for its rich cultural and religious diversity. It has been a land where several religions have flourished for centuries.
- Throughout its history, India has been home to various religions such as Hinduism, Islam, Christianity, Sikhism, Buddhism, Jainism, and many others.
- The Indian subcontinent has witnessed the rise and spread of these religions, resulting in a diverse religious landscape.

Secularism in India:
- The concept of secularism is enshrined in the Indian Constitution, which guarantees equal rights and freedom of religion to all its citizens.
- The framers of the Constitution aimed to create a society that respects and values all religions without favoring any particular religion.
- The idea of secularism in India promotes religious harmony and ensures that the state remains neutral in matters of religion.

Constitutional Provisions:
- The Indian Constitution, under Article 25-28, provides for the freedom of religion.
- Article 25 guarantees individuals the right to freely profess, practice, and propagate any religion.
- Article 26 grants religious denominations the right to manage their own affairs in matters of religion.
- Article 27 prohibits the state from levying taxes for promoting or maintaining any particular religion.
- Article 28 ensures that no religious instruction is provided in educational institutions wholly funded by the state.

Implications:
- By not declaring any official religion, India embraces the principles of secularism and respects the religious diversity within its borders.
- This approach allows individuals to have the freedom to practice and follow their own religion without any interference from the state.
- It fosters a sense of inclusivity and tolerance, promoting social harmony among people of different faiths.

Conclusion:
In conclusion, the official religion of the state in India is None (option D) as enshrined in the Constitution. India's commitment to secularism ensures religious freedom and equal treatment for all its citizens, regardless of their religious beliefs. This approach has played a significant role in maintaining the religious harmony and diversity that India is known for.

Ofcourse none