## **Core Concept**
The Couple Protection Rate (CPR) is a measure of the percentage of couples of reproductive age using some form of contraception. 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. An NRR of 1 indicates that, on average, a woman is replacing herself with one daughter, which is essential for a stable population.

## **Why the Correct Answer is Right**
To achieve an NRR of 1, a significant proportion of couples must practice family planning effectively. The correct answer, **75%**, reflects the generally accepted estimate that a CPR of about 60-75% is needed to achieve replacement fertility levels, where the NRR equals 1. This is because not all contraceptive methods are 100% effective, and some pregnancies may still occur despite contraceptive use.

## **Why Each Wrong Option is Incorrect**
- **Option A: 25%** - This is too low because achieving an NRR of 1 requires a much higher level of contraceptive prevalence to effectively reduce the average family size to about two children per couple.
- **Option B: 50%** - While a CPR of 50% indicates significant use of contraception, it is generally considered insufficient to achieve an NRR of 1, given the effectiveness of various contraceptive methods and the desired family size.
- **Option D: 90%** - Although a high CPR is beneficial for achieving low fertility rates, a 90% CPR is more than what is typically required to reach an NRR of 1, indicating a level of contraceptive use that would likely result in below-replacement fertility.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that achieving a specific NRR, like 1, requires a multi-faceted approach including education, access to contraceptives, gender equality, and economic stability. The often-cited threshold for replacement fertility is a CPR of around 60-75%, but this can vary depending on the effectiveness of contraceptive methods used.

## **Correct Answer:** C. 75%