Who among the following had the shortest span in office as the Prime Minister of India?

Based on the tenures of the Prime Ministers listed, Chaudhary Charan Singh had the shortest span in office among the given options. He served for 170 days from July 28, 1979, to January 14, 1980 [2]. In comparison, Lal Bahadur Shastri served for approximately 1 year and 7 months, from June 9, 1964, until his death on January 11, 1966 [1]. Chandra Shekhar's tenure lasted roughly 7 months (223 days) from November 10, 1990, to June 21, 1991. H. D. Deve Gowda served for nearly 11 months, from June 1, 1996, to April 21, 1997 [2]. While Atal Bihari Vajpayee holds the record for the shortest overall tenure (13 or 16 days in his first term) and Gulzarilal Nanda served 13 days as acting PM, among the specific individuals provided in the options, Charan Singh's 170-day term is the shortest [2].

Sources

1. [2] https://www.pmsangrahalaya.gov.in/prime-ministers-of-india
2. [1] Introduction to the Constitution of India, D. D. Basu (26th ed.). > Chapter 35: TABLES > C. PRIME MINISTERS OF INDIA > p. 534