The ionisation potentials of Li and K are 5.4 and 4.3 eV respectively. The ionization potential of Na will be:

Options

A. 9.7 eV
B. 1.1 eV
C. 4.9 eV
D. cannot be calculated

Answer

To determine the ionization potential of sodium (Na) based on the given ionization potentials of lithium (Li) and potassium (K), we can follow these steps:

### Step-by-Step Solution:

1. **Understand Ionization Potential**:
- Ionization potential (or ionization energy) is the energy required to remove an electron from an atom in its gaseous state. It is measured in electron volts (eV).

2. **Identify Given Values**:
- Ionization potential of Lithium (Li) = 5.4 eV
- Ionization potential of Potassium (K) = 4.3 eV

3. **Recognize the Trend in Group 1 Elements**:
- In the periodic table, as we move down a group (from Li to Na to K), the ionization potential decreases. This is due to the increase in atomic size and the addition of electron shells, making it easier to remove the outermost electron.

4. **Establish the Position of Sodium (Na)**:
- Sodium (Na) is located between Lithium (Li) and Potassium (K) in Group 1 of the periodic table. Therefore, its ionization potential should logically fall between those of Li and K.

5. **Determine the Range for Sodium's Ionization Potential**:
- Since Li has a higher ionization potential (5.4 eV) and K has a lower ionization potential (4.3 eV), we can conclude:
\[ 4.3 \, \text{eV} < \text{Ionization Potential of Na} < 5.4 \, \text{eV} \]

6. **Evaluate the Options Provided**:
- The options given for the ionization potential of Na are:
- A) 9.7 eV
- B) 4.9 eV
- C) 1.1 eV
- D) Cannot be calculated
- From our analysis, the only option that fits within the range of 4.3 eV and 5.4 eV is 4.9 eV.

7. **Conclude the Answer**:
- Therefore, the ionization potential of Sodium (Na) is **4.9 eV**.

### Final Answer:
The ionization potential of Na is **4.9 eV**.