Which one of the following statements is incorrect in relation to ionisation enthalpy ?

Options

A. Ionization enthalpy increases for each successive valence shell electron
B. The greatest increase in ionization enthalpy is experienced on removal of electron from core of noble gas configuration
C. End of valence electrons is marked by a big jump in ionization enthalpy
D. Removal of electron from orbitals bearing lower n value is easier than from orbital having higher n value

Explanation

To determine which statement about ionization enthalpy is incorrect, we will analyze each statement step by step.

### Step 1: Understand Ionization Enthalpy
Ionization enthalpy (or ionization energy) is defined as the amount of energy required to remove an electron from an isolated gaseous atom. It generally increases with the removal of successive electrons due to increased effective nuclear charge experienced by the remaining electrons.

### Step 2: Evaluate Each Statement

1. **Statement 1**: "Ionization enthalpy increases for each successive valence shell electron."
- **Analysis**: This statement is true. As we remove electrons from the same shell, the effective nuclear charge increases, requiring more energy to remove each successive electron.

2. **Statement 2**: "Greater ionization energy is experienced on removal of an electron from the core of noble gas configuration."
- **Analysis**: This statement is also true. Noble gases have a stable electron configuration, and removing an electron from the core (inner shell) requires significantly more energy compared to removing a valence electron.

3. **Statement 3**: "End of valence electron is marked by a big jump in ionization enthalpy."
- **Analysis**: This statement is true as well. When all valence electrons are removed, the next electron to be removed comes from a more stable inner shell, leading to a large increase in ionization energy.

4. **Statement 4**: "Removal of electron from orbitals bearing lower n value is easier than from orbitals having higher n value."
- **Analysis**: This statement is incorrect. Electrons in lower n value orbitals (inner shells) are more tightly bound to the nucleus due to the stronger electrostatic attraction, making them harder to remove than electrons in higher n value orbitals (outer shells).

### Conclusion
The incorrect statement regarding ionization enthalpy is:
**Statement 4**: "Removal of electron from orbitals bearing lower n value is easier than from orbitals having higher n value."

### Final Answer
The answer to the question is **Statement 4**.

---