The long form of periodic table is based on

Options

A. Shape of the atom
B. Mass of the atom
C. Atomic number of the atom
D. Electronegativity

Answer

To determine what the long form of the periodic table is based on, we can follow these steps:

### Step 1: Understand the Options
We have four options to consider:
1. The shape of the atom
2. The mass of the atom
3. The atomic number of the atom
4. Electronegativity

### Step 2: Analyze Each Option
- **Option 1: The shape of the atom** - The shape of an atom does not determine its position in the periodic table.
- **Option 2: The mass of the atom** - Historically, some periodic tables were arranged by atomic mass, but this is not the basis for the long form of the periodic table.
- **Option 3: The atomic number of the atom** - The modern long form of the periodic table is arranged based on increasing atomic number, which is the number of protons in the nucleus of an atom.
- **Option 4: Electronegativity** - While electronegativity is an important property of elements, it does not dictate the arrangement of the periodic table.

### Step 3: Conclusion
After analyzing the options, we conclude that the long form of the periodic table is based on the **atomic number of the atom**. Therefore, the correct answer is:
**Option 3: The atomic number of the atom.**