Second ionisation potential of `Li,Be,B` is in the order:

Options

A. `Li gt Be gt B`
B. `Li gt B gt Be`
C. `Be gt Li gt B`
D. `B gt Be gt Li`

Answer

To determine the order of the second ionization potential of lithium (Li), beryllium (Be), and boron (B), we need to analyze the electronic configurations and the stability of the resulting ions after the removal of electrons. Here’s a step-by-step solution:

### Step 1: Understand Ionization Potential
The second ionization potential (IP) is the energy required to remove a second electron from a positively charged ion. It is influenced by the stability of the resulting ion after the first electron has been removed.

### Step 2: Write the Electronic Configurations
- **Lithium (Li)**: The electronic configuration is \(1s^2 2s^1\). After the first ionization, it becomes \(Li^+\) with configuration \(1s^2\).
- **Beryllium (Be)**: The electronic configuration is \(1s^2 2s^2\). After the first ionization, it becomes \(Be^+\) with configuration \(1s^2 2s^1\).
- **Boron (B)**: The electronic configuration is \(1s^2 2s^2 2p^1\). After the first ionization, it becomes \(B^+\) with configuration \(1s^2 2s^2\).

### Step 3: Analyze the Stability of the Resulting Ions
- **For Li**: After the first ionization, \(Li^+\) has a stable noble gas configuration (\(1s^2\)). Removing another electron from this stable configuration requires a significant amount of energy.
- **For Be**: After the first ionization, \(Be^+\) has a configuration of \(1s^2 2s^1\). Removing another electron from the \(2s\) orbital, which is already stable, requires a considerable amount of energy.
- **For B**: After the first ionization, \(B^+\) has a configuration of \(1s^2 2s^2\). Removing an electron from the \(2p\) orbital is easier because it is less stable compared to the filled \(2s\) orbital.

### Step 4: Compare the Ionization Potentials
- The second ionization potential will be highest for beryllium because it involves removing an electron from a stable \(2s^1\) configuration.
- The second ionization potential for lithium will be next, as removing an electron from the stable \(1s^2\) configuration requires more energy than removing from \(2p\) in boron.
- The second ionization potential for boron will be the lowest because it involves removing an electron from a \(2p\) orbital, which is less stable than the \(2s\) orbital.

### Conclusion
Thus, the order of the second ionization potential is:
**Be > Li > B**