Modern periodic table is based on which of the following property of elements ?

Options

A. Atomic number
B. Atomic mass
C. Electronegativity
D. Electron affinity

Explanation

To solve the question "Modern periodic table is based on which of the following property of elements?" we will analyze the options provided: atomic number, atomic mass, electronegativity, and electron affinity.

### Step-by-Step Solution:

1. **Understanding the Modern Periodic Table**:
The modern periodic table organizes elements in a systematic way. It consists of rows (periods) and columns (groups) where elements are arranged based on certain properties.

**Hint**: Think about how elements are organized in the periodic table.

2. **Identifying the Basis of Arrangement**:
The modern periodic table is primarily arranged according to the atomic number of the elements. The atomic number is defined as the number of protons (or electrons) in an atom.

**Hint**: Recall what atomic number represents in terms of atomic structure.

3. **Explaining Atomic Number**:
The atomic number determines the position of an element in the periodic table. For example, hydrogen has an atomic number of 1, helium has 2, lithium has 3, and so on. This increasing order reflects the arrangement of elements in the table.

**Hint**: Consider how the periodic table progresses from one element to the next.

4. **Evaluating Other Options**:
- **Atomic Mass**: The earlier periodic table by Mendeleev was based on atomic mass, but it had limitations. The modern periodic table corrects these issues by using atomic number instead.
- **Electronegativity**: This is a property related to how atoms attract electrons in a bond but does not determine the arrangement in the periodic table.
- **Electron Affinity**: This refers to the energy change when an electron is added to a neutral atom, which is also not a basis for the arrangement in the periodic table.

**Hint**: Think about the definitions of these properties and how they relate to the periodic table.

5. **Conclusion**:
Based on the analysis, the modern periodic table is based on the atomic number of elements. Therefore, the correct answer is **atomic number**.

### Final Answer:
The modern periodic table is based on the property of **atomic number**.