Explanation:

A state of emergency in India can be declared under various articles of the Constitution, primarily Article 352 (National Emergency), Article 356 (State Emergency/President's Rule), and Article 360 (Financial Emergency). * **Correct Option (D) 1975:** The most significant and controversial state of internal emergency in India was declared by President Fakhruddin Ali Ahmed on June 25, 1975, on the advice of Prime Minister Indira Gandhi. This emergency lasted for 21 months, until March 21, 1977, and led to widespread arrests, censorship, and suspension of civil liberties. It is a pivotal event in India's post-independence political history. * **Incorrect Option (A) 1972:** While the early 1970s were a period of political and economic challenges, the specific internal emergency referred to in the question was not declared in 1972. India was involved in the Bangladesh Liberation War in 1971, which led to a national emergency, but the internal emergency was later. * **Incorrect Option (B) 1973:** The year 1973 did not witness the declaration of the internal emergency. The political climate was tense, but the official declaration occurred later. * **Incorrect Option (C) 1974:** The year 1974 was marked by significant political unrest, including the Bihar Movement and a railway strike, which contributed to the conditions leading to the emergency. However, the actual declaration was made in the subsequent year.