Periodicity in the properties of elements in modern periodic table is due to

Options

A. a regular increase in atomic weight of elements
B. periodicity in the electronic configuration of atoms of elements
C. successive increases in the atomic number of elements
D. existence of families of elements.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the reason for the periodicity in the properties of elements in the modern periodic table.

2. **Analyzing the Options**: We have four options to consider:
- A) A regular increase in the atomic weights of elements.
- B) Periodicity in the electronic configuration of atoms of elements.
- C) Successive increases in the atomic number of elements.
- D) Existence of families of elements.

3. **Evaluating Option A**: The first option suggests that periodicity is due to a regular increase in atomic weights. However, chemical properties do not depend solely on atomic weights. Thus, this option is incorrect.

4. **Evaluating Option B**: The second option states that periodicity in the electronic configuration of atoms leads to periodicity in the properties of elements. This is a strong candidate because elements in the same group have similar electronic configurations, particularly in their outermost shell, which influences their chemical behavior.

5. **Evaluating Option C**: The third option mentions successive increases in atomic number. While the modern periodic table is indeed arranged by atomic number, this does not directly explain the periodicity in properties. Therefore, this option is also not correct.

6. **Evaluating Option D**: The fourth option refers to the existence of families of elements. While families (or groups) do exhibit similar properties, this is a result of their electronic configuration rather than a direct cause of periodicity.

7. **Conclusion**: The most accurate explanation for the periodicity in the properties of elements in the modern periodic table is given by Option B: "Periodicity in the electronic configuration of atoms of elements." This periodicity in electronic configuration leads to similar chemical properties among elements in the same group.

**Final Answer**: The periodicity in the properties of elements in the modern periodic table is due to periodicity in the electronic configuration of atoms of elements (Option B).

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