The correct order in which the first ionisation potential increases is

Options

A. K, Be, Na
B. Be, Na, K
C. Na, K, Be
D. K, Na, Be

Explanation

To determine the correct order in which the first ionization potential increases among the elements sodium (Na), beryllium (Be), and potassium (K), we need to consider the periodic trends in ionization energy.

### Step-by-Step Solution:

1. **Understand Ionization Energy**:
Ionization energy is the energy required to remove the outermost electron from an atom in its gaseous state. It generally increases across a period and decreases down a group in the periodic table.

2. **Identify the Elements**:
We are given three elements: Sodium (Na), Beryllium (Be), and Potassium (K).
- Sodium (Na) is in Group 1 (alkali metals).
- Beryllium (Be) is in Group 2 (alkaline earth metals).
- Potassium (K) is also in Group 1 but is below sodium in the periodic table.

3. **Analyze Their Positions**:
- Beryllium (Be) is located higher in the periodic table and is a Group 2 element, which generally has a higher ionization energy than Group 1 elements.
- Sodium (Na) is below lithium and has a lower ionization energy than beryllium.
- Potassium (K) is below sodium and has a lower ionization energy than sodium.

4. **Determine the Trend**:
- As we move down a group (from Be to Na to K), the ionization energy decreases.
- Therefore, the order from highest to lowest ionization energy is: Be > Na > K.

5. **Establish the Correct Order of Increasing Ionization Energy**:
- Since we are looking for the order in which the first ionization potential increases, we can write it as:
- K < Na < Be

### Final Answer:
The correct order in which the first ionization potential increases is: **K < Na < Be**.