The infant mortality rate is the number of of deaths of babies before the age of:

one year per 1000 live births

The correct answer is Option (4) → one year per 1000 live births

The infant mortality rate is the number of deaths of babies before the age of one year per 1000 live births. Likewise, the maternal mortality rate is the number of women who die in childbirth per 1,00,000 live births.