Choose the correct statement/statements regarding Modern periodic table

Options

A. Actinoids are placed in main body of periodic table
B. Chemical properties are periodic function of atomic number
C. In periodic table, 18 group are present
D. 7th period is incomplete

Answer

To solve the question regarding the correct statements about the Modern Periodic Table, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Option 1: Actinoids are placed in the main body of the periodic table.**
- This statement is **incorrect**. The actinoids, along with the lanthanoids, are placed at the bottom of the periodic table, separate from the main body. They are not part of the S, P, or D blocks that make up the main body of the table.

2. **Option 2: Chemical properties are a periodic function of atomic number.**
- This statement is **correct**. In the modern periodic table, the chemical properties of elements are periodic functions of their atomic numbers, meaning that as you move across a period or down a group, the properties change in a predictable manner based on atomic number.

3. **Option 3: In the periodic table, the 18th group is present.**
- This statement is **correct**. The modern periodic table includes 18 groups, with the 18th group consisting of the noble gases, which are known for their lack of reactivity.

4. **Option 4: The 7th period is incomplete.**
- This statement is **correct**. The 7th period of the periodic table is considered incomplete because not all the elements in this period have been discovered or fully studied, leading to gaps in our understanding.

### Conclusion:
The correct statements regarding the Modern Periodic Table are:
- Option 2: Chemical properties are a periodic function of atomic number.
- Option 3: In the periodic table, the 18th group is present.
- Option 4: The 7th period is incomplete.