Which of the following statements about the modern periodic table is correct ?

Options

A. It has 18 horizontal rows known as periods
B. It has 7 vertical columns rows known as periods
C. It has 18 vertical columns known as groups
D. It has 7 horizontal rows known as groups

Explanation

To determine which statement about the modern periodic table is correct, we can analyze the characteristics of the table step by step.

### Step-by-Step Solution:

1. **Understanding the Structure of the Modern Periodic Table**:
- The modern periodic table is organized into vertical columns and horizontal rows.

2. **Identifying Vertical Columns (Groups)**:
- There are **18 vertical columns** in the modern periodic table, which are referred to as **groups**. Each group contains elements that have similar chemical properties.

3. **Identifying Horizontal Rows (Periods)**:
- There are **7 horizontal rows** in the modern periodic table, known as **periods**. Each period represents a different energy level of electrons.

4. **Analyzing the Statements**:
- The statements provided need to be evaluated based on the correct definitions of groups and periods.
- **Statement 1**: "It has seven vertical columns known as periods." - This is incorrect.
- **Statement 2**: "It has 18 horizontal rows known as periods." - This is incorrect.
- **Statement 3**: "It has 18 vertical columns known as periods." - This is incorrect; it should state "groups."
- **Statement 4**: "It has four horizontal rows known as groups." - This is incorrect.

5. **Identifying the Correct Statement**:
- The correct statement about the modern periodic table is that it has **18 vertical columns known as groups** and **7 horizontal rows known as periods**. However, none of the provided statements accurately reflect this.

### Conclusion:
The correct answer based on the information provided should emphasize that there are **18 groups** and **7 periods**. If the question is asking for the correct statement and one of the options states that there are **18 vertical columns known as groups**, that would be the correct choice.