**Core Concept**
Pulse Polio Immunization (PPI) is a mass campaign to administer Oral Poliovirus Vaccine (OPV) to children in areas with high polio prevalence, aiming to interrupt the transmission of wild poliovirus.

**Why the Correct Answer is Right**
The goal of PPI is to create a barrier of immunity in the population, thereby preventing the spread of wild poliovirus. OPV is administered to children under 5 years of age, as they are the primary reservoir of the virus. This strategy is particularly effective in areas with low vaccination coverage, where a single dose of OPV can provide protection against polio for up to 12 months.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the target population for PPI is not adults, who may have already developed immunity to polio through natural infection or previous vaccination.
**Option B:** This option is incorrect as the primary goal of PPI is not to induce seroconversion, but rather to create a barrier of immunity in the population to prevent the spread of wild poliovirus.
**Option C:** This option is incorrect as the target age group for PPI is not limited to infants, but extends up to 5 years of age to ensure that all children in the population are protected against polio.

**Clinical Pearl / High-Yield Fact**
Pulse Polio Immunization campaigns are typically conducted during peak poliovirus transmission seasons, which can vary depending on the region, but often coincide with the rainy season when the virus is more likely to spread.

**Correct Answer: D. Children under 5 years of age.**

✓ Correct Answer: A. All children between 0-5 years of age on a single day, irrespective of their previous immunization status