## **Core Concept**
The Net Reproduction Rate (NRR) measures the number of daughters a woman would have in her lifetime under the prevailing age-specific fertility and mortality rates, indicating the extent to which a generation replaces itself. A NRR of 1 implies that, on average, a woman has just enough daughters to replace herself, thus sustaining a stable population size over time, assuming no changes in mortality rates. The Couple Protection Rate (CPR) refers to the percentage of couples of reproductive age using some form of modern or traditional contraceptive method.

## **Why the Correct Answer is Right**
To achieve a NRR of 1, a significant portion of couples must be practicing effective family planning to reduce the average number of children per woman to approximately 2.1 (the replacement level fertility rate, considering mortality rates). A CPR of **75%** is often cited as a threshold that, if achieved and sustained, can lead to a NRR of 1 or close to it, given that it signifies a high level of contraceptive prevalence and, consequently, a lower total fertility rate. This relationship, however, can vary depending on the effectiveness of the contraceptive methods used and the desired family size.

## **Why Each Wrong Option is Incorrect**
- **Option A:** A CPR of less than 50% is typically associated with high fertility rates and would not lead to a NRR of 1. Such a low level of contraceptive use would likely result in a much higher NRR, indicating rapid population growth.
- **Option B:** While a CPR of 60% indicates a significant level of contraceptive use, it might not be sufficient to bring the NRR down to 1, especially if the methods used are not highly effective or if there is a high unmet need for family planning.
- **Option D:** A CPR of more than 90% would likely result in a NRR significantly below 1, potentially leading to population decline over time, as it indicates a very high level of contraceptive prevalence.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that achieving and maintaining a NRR of 1 requires not just a high CPR but also that the contraceptive methods used are effective and appropriately chosen by couples. Additionally, factors such as maternal and child health, education, and economic status play crucial roles in influencing fertility rates and the success of family planning programs.

## **Correct Answer:** .