**Core Concept**
Demonstration is a key teaching method in public health and community medicine, particularly when teaching mothers about using Oral Rehydration Solution (ORS). This method involves showing the actual process of rehydration to ensure that the mothers understand and can replicate it correctly.

**Why the Correct Answer is Right**
Demonstration is the best method for teaching mothers about using ORS because it allows for immediate feedback and visual understanding. When a mother sees a healthcare worker or peer demonstrate how to prepare and administer ORS, she can observe the correct technique, ask questions, and practice alongside. This interactive approach helps build confidence and reduces the risk of errors. Moreover, demonstration is more effective than other methods, such as group discussion or lecture, because it caters to different learning styles and provides a hands-on experience.

**Why Each Wrong Option is Incorrect**
**Option A:** Group discussion may not be effective in teaching mothers about using ORS, as it relies on verbal communication and may not provide a clear understanding of the process.
**Option C:** Lecture is a passive teaching method that may not engage mothers and may not provide the necessary hands-on experience to ensure proper understanding.
**Option D:** Flannel graph, a visual aid used in teaching, may not be effective in teaching mothers about using ORS, as it does not provide a real-life demonstration of the process.

**Clinical Pearl / High-Yield Fact**
When teaching mothers about using ORS, it is essential to demonstrate the correct technique, including measuring the correct amount of water and electrolyte solution, mixing the solution correctly, and administering it to the child.

**✓ Correct Answer: B. Demonstration**