## Core Concept
The Pulse Polio Immunization (PPI) program was a nationwide campaign aimed at eradicating poliomyelitis (polio) from India. It involved mass immunization of children under the age of five against poliovirus. The program was critical in controlling and eventually eliminating polio.

## Why the Correct Answer is Right
The Pulse Polio Immunization program was launched in 1994, marking a significant effort by the Indian government to immunize all children under five years of age against poliovirus. This program was a response to the high incidence of polio cases in India during the early 1990s. The campaign involved administering oral poliovirus vaccine (OPV) to children in two rounds, usually in January and February of each year, supplemented by immunization drives throughout the year.

## Why Each Wrong Option is Incorrect
* **Option A:** 1984 - This is too early for the introduction of the Pulse Polio Immunization program on a national scale. While there were polio immunization efforts before 1994, the PPI program as a comprehensive national strategy began later.
* **Option B:** 1990 - Although close, this is still a couple of years before the actual launch of the PPI program. The groundwork for such a program might have been laid around this time, but the nationwide campaign started in 1994.
* **Option D:** 1999 - This is too late, as the PPI program was already underway by 1994 and continued its efforts until polio was declared eliminated in India.

## Clinical Pearl / High-Yield Fact
A key fact to remember is that India was declared polio-free in 2014, marking the culmination of the Pulse Polio Immunization program's efforts. This achievement underscores the importance of mass immunization campaigns in controlling infectious diseases.

**Correct Answer: C. 1994.**