Metalloids are

Options

A. alloys of alkali metals with other metals.
B. colloids of metals
C. element having some properties of both metals and non-metals .
D. metals heavier than lead.

Explanation

**Step-by-Step Solution:**

1. **Definition of Metalloids**:
Metalloids are chemical elements that exhibit properties intermediate between metals and non-metals. They are not strictly classified as either, which makes their definition somewhat ambiguous.

2. **Characteristics of Metalloids**:
Metalloids typically have a mixture of properties. For example, they may conduct electricity like metals but can be brittle like non-metals. This duality allows them to be useful in various applications, particularly in semiconductors.

3. **Commonly Recognized Metalloids**:
The six most commonly recognized metalloids are:
- Boron (B)
- Silicon (Si)
- Germanium (Ge)
- Arsenic (As)
- Antimony (Sb)
- Tellurium (Te)

4. **Less Commonly Recognized Metalloids**:
There are also elements that are less commonly classified as metalloids, including:
- Carbon (C)
- Aluminum (Al)
- Selenium (Se)
- Polonium (Po)
- Astatine (At)

5. **Conclusion**:
Based on the definitions and properties discussed, the correct classification of metalloids aligns with the statement that they are elements having some properties of both metals and non-metals.

**Final Answer**: Metalloids are elements that have some properties of both metals and non-metals.

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