In India, which of the following is NOT a factor responsible for reduction of birth rate in the 21st century?

Efficient sanitation

The factor that is NOT responsible for the reduction of the birth rate in the 21st century is: Efficient sanitation

While efficient sanitation can contribute to overall public health and well-being, it is not directly linked to reducing birth rates. The other options—increased female literacy, awareness and acceptance of family planning, and an increase in the mean age of marriage—are all known factors associated with the reduction of birth rates in India.