The statement that is not correct for period orbit of elements is:

Options

A. The properties of elements are periodic function atomic numbers
B. Non-metallic elements are less in number that elements
C. For transition elements, the 3d-orbitals are fill electrons after 3p-orbital and before 4s-orbital
D. The first ionisation enthalpies of element is increase with increase in atomic numbers as we in period

Explanation

To determine which statement is not correct regarding the periodic properties of elements, we need to analyze each option provided in the question. Let's break down the statements one by one.

### Step-by-Step Solution:

1. **Understanding the Periodic Function of Elements**:
- The first statement claims that the properties of elements are a periodic function of atomic number. This is true as the periodic law states that the properties of elements are periodic functions of their atomic numbers.

2. **Non-Metallic Elements**:
- The second statement suggests that non-metallic elements are less in number than metallic elements. This statement is also correct. In the periodic table, there are significantly more metals compared to non-metals.

3. **Filling of Orbitals**:
- The third statement discusses the filling of 3d and 4s orbitals. It states that the 3d orbitals are filled after the 3p and before the 4s. This statement is incorrect. According to the Aufbau principle, the 4s orbital is filled before the 3d orbital. Therefore, the correct order of filling is 1s, 2s, 2p, 3s, 3p, 4s, and then 3d.

4. **Ionization Enthalpy**:
- The fourth statement claims that the first ionization enthalpy of elements increases with atomic number in a period. This is correct. As we move across a period, the effective nuclear charge increases, leading to higher ionization energy.

### Conclusion:
After analyzing all the statements, we conclude that the **third statement** is the incorrect one. It incorrectly describes the order of filling of the 3d and 4s orbitals.

### Final Answer:
The statement that is not correct for the periodic orbit of elements is: **"The 3d orbitals are filled after the 3p and before the 4s."**

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