Which of the following leaves a crushable black bead on burning?

Options

A. Cotton
B. Silk
C. Nylon
D. Acrylic

Explanation

To solve the question "Which of the following leaves a crushable black bead on burning?", we need to analyze the options provided and understand the characteristics of the materials mentioned.

### Step-by-Step Solution:

1. **Identify the Options**:
- We need to know the options given in the question. The options mentioned in the video transcript are:
- Silk
- Cotton
- Nylon
- Acrylic

2. **Understand the Properties of Each Material**:
- **Silk**: A natural fiber derived from silkworms. When burned, silk produces a black bead.
- **Cotton**: A natural fiber from cotton plants. It burns to ash and does not leave a bead.
- **Nylon**: A synthetic fiber made from petrochemicals. It melts and burns, leaving a hard residue but not a bead.
- **Acrylic**: Another synthetic fiber that burns and leaves a hard residue, not a bead.

3. **Determine Which Material Leaves a Black Bead**:
- From our analysis, we see that **silk** is the only material that, when burned, leaves a crushable black bead.

4. **Conclusion**:
- Therefore, the answer to the question is **Silk**.

### Final Answer:
Silk leaves a crushable black bead on burning.

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