In the modern periodic table, which one is most correct about a period?

Options

A. The first element is an alkali metal, and the last element is a halogen.
B. The first element is a noble gas, and the last one is an alkali metal.
C. The first element is an alkali metal, and the last element is a noble gas.
D. Each element is a nonmetal.

Explanation

To determine which statement is most correct about a period in the modern periodic table, we will analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding the Structure of the Periodic Table**:
- The modern periodic table is organized into periods (rows) and groups (columns). Each period contains elements with increasing atomic numbers.

2. **Analyzing Each Option**:
- **Option 1**: "The first element is an alkali metal and the last element is a halogen."
- The first element in a period is indeed an alkali metal (e.g., Lithium in Period 2). However, the last element in a period is a noble gas (e.g., Neon in Period 2), not a halogen. Therefore, this statement is **incorrect**.

- **Option 2**: "The first element is a noble gas and the last one is an alkali metal."
- This statement is incorrect because the first element in a period is an alkali metal, not a noble gas. Hence, this statement is also **incorrect**.

- **Option 3**: "The first element is an alkali metal and the last element is a noble gas."
- This statement is correct. The first element in a period is an alkali metal (e.g., Lithium in Period 2), and the last element is a noble gas (e.g., Neon in Period 2). Therefore, this statement is **correct**.

- **Option 4**: "Each element is a nonmetal."
- This statement is incorrect because a period contains a mix of metals, nonmetals, and metalloids. Not all elements in a period are nonmetals. Thus, this statement is **incorrect**.

3. **Conclusion**:
- After analyzing all the options, the most correct statement about a period in the modern periodic table is **Option 3**: "The first element is an alkali metal and the last element is a noble gas."

### Final Answer:
The most correct statement about a period in the modern periodic table is that the first element is an alkali metal and the last element is a noble gas (Option 3).

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