Significance of 14 September
The date 14 September is significant in India as it marks the day when Hindi was adopted as the official language of the Republic of India. This decision was made by the Constituent Assembly on September 14, 1949.

Reasons Why 14 September 1949 is Important
- Official Language Adoption: Hindi was chosen to promote unity in a country with diverse languages and cultures. This decision aimed to ensure effective communication within the government and among the populace.
- Cultural Identity: By adopting Hindi, India aimed to strengthen its cultural identity. Hindi is spoken by a large portion of the population and serves as a bridge between various linguistic groups.
- Constitutional Recognition: The adoption of Hindi as an official language was enshrined in the Indian Constitution, which came into effect on January 26, 1950. This laid the foundation for its usage in official communication and education.

Misconceptions About Other Dates
- 14 September 1948: This date does not hold significant relevance in terms of language adoption.
- 14 September 1947: This date is too early, as it was before India became a republic.
- 15 August 1949: This date is incorrect as it refers to India's independence, which was celebrated on August 15, 1947.

Conclusion
Thus, the correct answer is option 'B', 14 September 1949, as it marks a pivotal moment in India's linguistic history and cultural integration.