What is the basis of the long form of the periodic table?

Options

A. Atomic mass
B. Atomic number
C. Atomic size
D. Metallic and nonmetallic character

Explanation

### Step-by-Step Solution:

1. **Understanding the Periodic Table**: The periodic table is a systematic arrangement of elements based on their properties. It helps in understanding the relationships between various elements.

2. **Modern Periodic Law**: The modern periodic law, proposed by Dmitri Mendeleev, states that the physical and chemical properties of elements are periodic functions of their atomic numbers. This means that when elements are arranged in order of increasing atomic number, elements with similar properties appear at regular intervals.

3. **Atomic Number Definition**: The atomic number (denoted by the symbol Z) is defined as the number of protons in the nucleus of an atom. It also equals the number of electrons in a neutral atom. The atomic number is fundamental in determining the identity of an element.

4. **Basis of the Long Form of the Periodic Table**: Since the modern periodic law is based on atomic number, the long form of the periodic table is constructed using atomic numbers. This arrangement allows for a clearer representation of the periodic trends and properties of the elements.

5. **Conclusion**: Therefore, the basis of the long form of the periodic table is the atomic number, which corresponds to option B.

### Final Answer:
The basis of the long form of the periodic table is the atomic number (Option B).

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