Name one metalloid of period 3.

Explanation

To solve the question of naming one metalloid of period 3, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of a Metalloid**:
- A metalloid is a chemical element that exhibits properties of both metals and nonmetals. They are also referred to as semi-metals.

2. **Identify the Elements in Period 3**:
- The elements in period 3 of the periodic table are: Sodium (Na), Magnesium (Mg), Aluminum (Al), Silicon (Si), Phosphorus (P), Sulfur (S), Chlorine (Cl), and Argon (Ar).

3. **Determine Which of These Elements are Metalloids**:
- From the list of period 3 elements, we need to identify which one is classified as a metalloid. In period 3, Silicon (Si) is the only element that exhibits metalloid properties.

4. **Conclude the Answer**:
- Therefore, one metalloid of period 3 is Silicon (Si).

### Final Answer:
Silicon (Si) is one metalloid of period 3.

---