Which one of the following materials cannot be used to make a lens ?

Options

A. Water
B. Glass
C. Plastic
D. Clay

Explanation

To determine which material cannot be used to make a lens, we need to analyze the properties of various materials. A lens is typically made from materials that can refract light, allowing it to converge or diverge. Common materials used for lenses include glass and plastic. Let's evaluate the options step by step.

### Step 1: Identify Common Lens Materials
Lenses are usually made from materials that can bend light effectively. The most common materials include:
- **Glass**: Widely used for optical lenses due to its clarity and ability to refract light.
- **Plastic**: Also used for lenses, especially in lightweight applications like eyeglasses and cameras.

### Step 2: Consider Other Materials
Now, we need to consider other materials that might not be suitable for lens-making:
- **Water**: Water can act as a lens under certain conditions, such as in a drop of water, but it is not a solid material used for traditional lenses.
- **Metal**: Metals are generally opaque and do not allow light to pass through, making them unsuitable for lens-making.

### Step 3: Determine the Answer
Among the materials mentioned, the one that cannot be used to make a lens is **metal**. Metals do not refract light and are not transparent, which are essential properties for lens materials.

### Final Answer
**Metal cannot be used to make a lens.**

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