Pick the odd one out:

Options

A. titanium
B. bronze
C. solder
D. gun metal

Explanation

**Step-by-Step Solution:**

1. **Identify the Options**: The question asks to pick the odd one out from a list of materials. The materials mentioned are bronze, solder, gun metal, and titanium.

2. **Define Each Material**:
- **Bronze**: An alloy made primarily of copper and tin.
- **Solder**: An alloy used to join metal pieces, typically made of tin and lead.
- **Gun Metal**: An alloy consisting mainly of copper, tin, and zinc, used for making guns and other machinery.
- **Titanium**: A pure metal, known for its strength and resistance to corrosion.

3. **Classify the Materials**:
- **Alloys**: Bronze, solder, and gun metal are all alloys, meaning they are mixtures of two or more metals.
- **Pure Metal**: Titanium is a pure metal, consisting only of titanium atoms.

4. **Determine the Odd One Out**: Since bronze, solder, and gun metal are alloys, while titanium is a pure metal, titanium is the odd one out.

5. **Conclusion**: The odd one out is titanium because it is not an alloy, whereas the others are.

**Final Answer**: Titanium

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