State Periodic Law on which the Modern Periodic Table is based.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Periodic Law**: The modern periodic table is based on a specific periodic law. This law states that the properties of elements are periodic functions of their atomic numbers.

2. **Defining Atomic Number**: The atomic number is defined as the number of protons in the nucleus of an atom. In a neutral atom, the atomic number also equals the number of electrons.

3. **Arrangement of Elements**: In the modern periodic table, elements are arranged in increasing order of their atomic numbers. This means that as you move across the table, the atomic number increases sequentially.

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