Which of the following statement `(s)` is`//`are correct ?

Options

A. Mendeleev's periodic law was based on atomic number of the
element.
B. Zero group was not present in the periodic table when Mendeleev presented it.
C. The effective nuclear charge `(Z_(eff))` is the atomic number minus shielding effect.
D. There are four transition series in the periodic table each one
consists of `10` elements.

Explanation

To determine which of the statements provided are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: Mendeleev's periodic law was based on the atomic number of the element.**
- **Analysis:** This statement is incorrect. Mendeleev's periodic law was based on the atomic weights of the elements, not their atomic numbers. He arranged the elements in order of increasing atomic weight and observed that their properties were periodic functions of these weights.
- **Conclusion:** Statement 1 is **incorrect**.

2. **Statement 2: Zero group was not present in the periodic table when Mendeleev was alive.**
- **Analysis:** This statement is correct. When Mendeleev created his periodic table, only 63 elements were known, and the noble gases (which belong to the zero group) were discovered later. Therefore, the zero group was not included in his periodic table.
- **Conclusion:** Statement 2 is **correct**.

3. **Statement 3: The effective nuclear charge is the atomic number minus the shielding effect.**
- **Analysis:** This statement is correct. The effective nuclear charge (Z_eff) can be calculated using the formula Z_eff = Z - σ, where Z is the atomic number and σ is the shielding constant (or shielding effect). This reflects the net positive charge experienced by an electron in a multi-electron atom.
- **Conclusion:** Statement 3 is **correct**.

4. **Statement 4: There are four transition series in the periodic table, each one consists of 10 elements.**
- **Analysis:** This statement is correct. The four transition series are the 3D, 4D, 5D, and 6D series, and each series contains 10 elements. The D-block elements fill the d-orbitals, which can hold a maximum of 10 electrons.
- **Conclusion:** Statement 4 is **correct**.

### Final Conclusion:
The correct statements are:
- Statement 2: Zero group was not present in the periodic table when Mendeleev was alive.
- Statement 3: The effective nuclear charge is the atomic number minus the shielding effect.
- Statement 4: There are four transition series in the periodic table, each one consists of 10 elements.

### Summary of Correct Statements:
- **Correct Statements:** 2, 3, and 4
- **Incorrect Statement:** 1