Concept:
Infant Mortality Rate (IMR) is an important indicator of the health conditions of a country. It measures the number of infants who die before reaching the age of one year for every 1000 live births in a given year.
Step 1: {\color{red}Understand the definition of Infant Mortality Rate.}
Infant Mortality Rate refers to the number of deaths of infants under the age of one year per 1000 live births in a particular year.
Step 2: {\color{red}Identify the correct value.}
Since the definition clearly mentions children who die before completing one year of age, the blank should be filled with:
\[
One
\]
Step 3: {\color{red}Select the correct option.}
Therefore, the correct answer is Option (A).