Beryllium has higher ionisation enthalpy than boron.This can be explained as,

Options

A. Beryllium has higher size than boron hence its ionisation enthalpy is higher
B. Penetration of 2p-electrons to the nucleus is more than the 2s-electrons
C. It is easier to remove electron from 2p-orbital as compared to 2s-orbital due to more penetration of s-electrons
D. Ionisation energy increases in a period.

Answer

To explain why beryllium has a higher ionization enthalpy than boron, we can follow these steps:

### Step 1: Understand the Electronic Configuration
- Beryllium (Be) has the electronic configuration of \(1s^2 2s^2\).
- Boron (B) has the electronic configuration of \(1s^2 2s^2 2p^1\).

### Step 2: Identify the Valence Electrons
- Beryllium has 2 valence electrons in the 2s subshell.
- Boron has 3 valence electrons, with 2 in the 2s subshell and 1 in the 2p subshell.

### Step 3: Consider the Size of the Atoms
- Beryllium is smaller in size compared to boron. The atomic radius of beryllium is less than that of boron due to its higher nuclear charge, which pulls the electrons closer to the nucleus.

### Step 4: Analyze the Penetration Effect
- The penetration effect refers to how close an electron can get to the nucleus. Electrons in the s subshell (2s) have a greater penetration effect than those in the p subshell (2p).
- This means that the 2s electrons in beryllium are held more tightly by the nucleus compared to the 2p electrons in boron.

### Step 5: Compare the Ionization Energies
- Ionization energy is the energy required to remove an electron from an atom.
- Since the 2s electrons in beryllium are more tightly bound to the nucleus due to their greater penetration, it requires more energy to remove an electron from beryllium than from boron.

### Conclusion
- Therefore, beryllium has a higher ionization enthalpy than boron because its 2s electrons are more tightly held due to the penetration effect, making it more difficult to remove an electron compared to the 2p electrons in boron.