The correct answer is option 'C', Raj Narain vs Indira Gandhi. This case was a landmark case regarding election disputes and led to the imposition of emergency in India. The primary issue in this case was the validity of clause 4 of the 39th Amendment Act.

Background:
In the 1971 general elections, Indira Gandhi was re-elected as the Prime Minister of India. However, her victory was challenged by Raj Narain, an opposition candidate from the Rae Bareli constituency. Narain alleged that Gandhi had committed several electoral malpractices, including the use of government machinery for campaigning.

Key Issue:
The primary issue in this case was the validity of clause 4 of the 39th Amendment Act. This clause inserted Article 329-A into the Constitution, which stated that the election of the Prime Minister, President, and Speaker of Lok Sabha could not be challenged in courts.

Legal Proceedings:
The case was initially heard by the Allahabad High Court, which found Indira Gandhi guilty of electoral malpractices and declared her election void. This decision created a political crisis in the country, leading to widespread protests and demands for her resignation.

Supreme Court Judgment:
Both Indira Gandhi and Raj Narain appealed against the High Court's decision in the Supreme Court. The Supreme Court delivered its judgment on 7th November 1975. The court upheld the High Court's decision, stating that Indira Gandhi had indulged in corrupt practices during the election campaign.

Emergency Imposition:
Following the Supreme Court's judgment, Indira Gandhi faced immense political pressure and criticism. In order to retain power, she decided to impose a state of emergency in the country on 25th June 1975. During the emergency, civil liberties were suspended, and political opponents were arrested.

Aftermath:
The imposition of emergency led to widespread criticism and protests in the country. It was seen as a violation of democratic principles and an abuse of power. The emergency was finally lifted in 1977, and fresh elections were held, which resulted in the defeat of Indira Gandhi's party.

In conclusion, the case of Raj Narain vs Indira Gandhi was a landmark case regarding election disputes and led to the imposition of emergency in India. The primary issue in this case was the validity of clause 4 of the 39th Amendment Act, which inserted Article 329-A into the Constitution.