The modern periodic table is based on

Options

A. mass number
B. molecular mass
C. atomic radius
D. atomic number

Explanation

To solve the question regarding what the modern periodic table is based on, we can follow these steps:

1. **Understanding the Options**: The question provides four options:
- A) Mass number
- B) Molecular mass
- C) Atomic radius
- D) Atomic number

2. **Historical Context**: The modern periodic table was developed based on the work of several scientists, most notably Moseley. He established that the properties of elements are periodic functions of their atomic number rather than their mass number.

3. **Analyzing Each Option**:
- **Option A (Mass number)**: This is not the basis for the modern periodic table. Earlier tables were arranged by mass number, but this led to inconsistencies.
- **Option B (Molecular mass)**: This is not relevant to the arrangement of elements in the periodic table.
- **Option C (Atomic radius)**: While atomic radius can influence properties, it is not the basis for the arrangement of the periodic table.
- **Option D (Atomic number)**: Moseley’s work showed that elements should be arranged by atomic number, which reflects their properties more accurately.

4. **Conclusion**: Based on the analysis, the modern periodic table is based on atomic number, which corresponds to option D.

5. **Final Answer**: The modern periodic table is based on **atomic number** (Option D).