## **Core Concept**
The female condom, also known as an internal condom, is a barrier method of contraception designed for use by women. It is made of a thin, flexible pouch of polyurethane or nitrile and is inserted into the vagina before sexual intercourse to prevent pregnancy and reduce the risk of sexually transmitted infections (STIs).

## **Why the Correct Answer is Right**
The correct answer indicates a specific failure rate for the female condom. Typically, the failure rate of contraceptive methods is expressed in terms of the number of pregnancies per 100 users over a one-year period. The female condom has a relatively high failure rate compared to other contraceptive methods, such as intrauterine devices (IUDs) or oral contraceptives. A commonly cited failure rate for the female condom is around 21 pregnancies per 100 users in a year, which places it in the range of **C. 21 per 100**.

## **Why Each Wrong Option is Incorrect**
- **Option A:** A failure rate lower than what's commonly reported for the female condom would be incorrect. For instance, if option A suggests a rate much lower than 20 per 100, it would not align with the documented efficacy of the female condom.
- **Option B:** Similarly, if option B suggests a rate slightly lower or higher but not consistent with the known efficacy, it would be incorrect. For example, a rate of 5-10 per 100 is more characteristic of highly effective methods like IUDs or implants.
- **Option D:** If option D suggests a significantly higher failure rate than documented, such as 40 per 100 or more, it would not accurately reflect the performance of the female condom.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the effectiveness of the female condom can be influenced by proper use and insertion techniques. However, even with perfect use, its effectiveness is generally lower compared to other contraceptive methods. This method is still considered beneficial for its role in STI prevention.

## **Correct Answer: C. 21 per 100.**