Which of the following cannot be charged by friction, if held by hand ?

Options

A. a plastic scale
B. a copper rod
C. an inflated balloon
D. a woollen cloth

Answer

To solve the question "Which of the following cannot be charged by friction, if held by hand?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Charging by Friction**:
- Charging by friction occurs when two materials are rubbed together, causing electrons to transfer from one material to another. This can create a static charge on the materials involved.

2. **Identify the Materials**:
- The question likely provides a list of materials (e.g., rubber, glass, copper, plastic). We need to analyze each material to determine if it can be charged by friction.

3. **Determine Conductivity**:
- Materials can be classified as conductors or insulators:
- **Conductors** (like metals) allow electrons to flow freely.
- **Insulators** (like rubber or plastic) do not allow electrons to move freely.

4. **Analyze Each Option**:
- If a material is a conductor (like copper), any charge developed on it will quickly dissipate through the conductor and into the ground when held by hand. Therefore, it cannot retain a charge.
- If a material is an insulator, it can hold a charge when rubbed, as the charge does not flow away.

5. **Conclusion**:
- Among the options, the copper rod is a conductor. Therefore, it cannot be charged by friction when held by hand, as the charge will dissipate through the body to the ground.
- The other options (assuming they are insulators) can retain a charge when rubbed.

### Final Answer:
- The correct option is **B: Copper rod**.