**Core Concept**
The question is testing the knowledge of the most effective contraceptive method for a healthy newly married couple. The underlying principle is to identify a highly reliable and user-friendly contraceptive option that can be used consistently and effectively to prevent unplanned pregnancies.

**Why the Correct Answer is Right**
The most effective contraceptive method for a healthy newly married couple is the Intrauterine Device (IUD), specifically the copper IUD or the hormonal IUD (Mirena). The copper IUD works by releasing ions that are toxic to sperm, while the hormonal IUD releases levonorgestrel, which thickens cervical mucus to prevent sperm entry and also thins the uterine lining to prevent implantation. The high efficacy of IUDs is due to their long-term duration of action and minimal user error.

**Why Each Wrong Option is Incorrect**
**Option A:** Oral contraceptive pills (OCPs) are highly effective when taken correctly but have a high failure rate due to user error, such as missed doses or incorrect timing. They also have side effects and interactions with other medications.
**Option B:** Condoms are highly user-dependent and have a high failure rate due to slippage, breakage, or incorrect use. They also provide protection against sexually transmitted infections (STIs) but are not as effective as IUDs in preventing pregnancy.
**Option C:** Sterilization (vasectomy or tubal ligation) is a highly effective method but is typically considered for couples who have completed their family planning goals. It involves a surgical procedure, which may not be suitable for all individuals.

**Clinical Pearl / High-Yield Fact**
The most effective contraceptive methods are those that are highly reliable, user-friendly, and have a low failure rate. IUDs, implants, and sterilization procedures are highly effective options, while OCPs and condoms have a higher failure rate due to user error or other factors.

**Correct Answer:** C. Sterilization (vasectomy or tubal ligation)