**Core Concept**
The Net Reproductive Rate (NRR) is a demographic measure that estimates the average number of daughters a woman would have in her lifetime, assuming a stable population size. An NRR of 1 indicates a replacement-level fertility rate, where the population size remains stable. Achieving NRR=1 is crucial for population stabilization.

**Why the Correct Answer is Right**
Vasectomy is a highly effective, long-term male sterilization method that prevents sperm from reaching the ejaculate. With a failure rate of less than 1%, vasectomy is considered one of the most reliable forms of contraception. When a significant proportion of the male population undergoes vasectomy, it can lead to a rapid decline in birth rates and ultimately achieve an NRR of 1. This is because vasectomy is a permanent method, and once implemented, it does not require ongoing user compliance or maintenance.

**Why Each Wrong Option is Incorrect**
**Option A:** IUCD (Intrauterine Contraceptive Device) is an effective form of contraception, but it is not as permanent as vasectomy. IUCD failure rates are higher than vasectomy, and it may not be as widely accepted or adopted by the population, making it less effective in achieving NRR=1.

**Option B:** Condoms are a highly effective form of contraception when used correctly, but they have a higher failure rate compared to vasectomy. Condoms also require ongoing user compliance, which may not be as reliable as a permanent method like vasectomy.

**Option D:** Oral pills are a popular form of contraception, but they have a higher failure rate compared to vasectomy. Additionally, oral pills require ongoing user compliance, and their effectiveness can be affected by factors such as missed doses or interactions with other medications.

**Clinical Pearl / High-Yield Fact**
A key factor in achieving NRR=1 is the widespread adoption of permanent methods of contraception, such as vasectomy. This is because permanent methods do not require ongoing user compliance, making them more reliable and effective in the long term.

**✓ Correct Answer: C. Vasectomy**