The element having highest ionisation potential is 

Options

A. Ne
B. N
C. O
D. He

Answer

To determine the element with the highest ionization potential among the given options (neon, nitrogen, oxygen, and helium), we can follow these steps:

### Step 1: Understand Ionization Potential
Ionization potential (or ionization energy) is the energy required to remove an electron from an atom in its gaseous state. Generally, ionization energy increases across a period and decreases down a group in the periodic table.

**Hint:** Remember that ionization energy is influenced by the atomic structure and the position of the element in the periodic table.

### Step 2: Analyze the Given Elements
The elements provided are:
- Neon (Ne)
- Nitrogen (N)
- Oxygen (O)
- Helium (He)

**Hint:** Look at the position of each element in the periodic table to understand their trends in ionization energy.

### Step 3: Determine Their Positions
- Helium (He) is in Group 18 (Noble gases), Period 1.
- Neon (Ne) is in Group 18 (Noble gases), Period 2.
- Nitrogen (N) is in Group 15, Period 2.
- Oxygen (O) is in Group 16, Period 2.

**Hint:** Noble gases generally have higher ionization energies compared to other groups.

### Step 4: Compare Ionization Energies
- As we move from left to right in a period, ionization energy increases. Therefore, among nitrogen, oxygen, and neon, we would expect neon to have the highest ionization energy.
- However, helium, being a noble gas and located in the first period, has a very small atomic size and a strong attraction between the nucleus and the outermost electron.

**Hint:** Consider the size of the atom and the effective nuclear charge when comparing ionization energies.

### Step 5: Conclusion
Based on the trends in ionization energy:
- Helium has the highest ionization potential due to its small size and the strong attraction between the nucleus and the outermost electron.
- Therefore, the element with the highest ionization potential among the given options is **Helium (He)**.

**Final Answer:** Helium (He)