The correct answer is option 3: Sindhi. In 1967, Sindhi was added to the Eighth Schedule of the Indian Constitution through a Constitutional Amendment.

The Eighth Schedule of the Indian Constitution lists the languages recognized by the government of India for official purposes. As of now, it includes 22 languages. Sindhi is one of these recognized languages, having been added to the list in 1967.

It is important to note that the Eighth Schedule is periodically updated to accommodate the inclusion of new languages. These updates are made through Constitutional Amendments. Therefore, it is crucial to stay updated with the latest amendments to have accurate knowledge of the languages recognized in the Eighth Schedule.

To summarize, Sindhi was added to the Eighth Schedule by a Constitutional Amendment in 1967 and is recognized as one of the official languages in India.