Assertion: The first ionisation energy of `Be` is greater than that of `B`.
Reason: 2p-orbital is lower in energy than 2s-orbital.

Options

A. Statement-1 is true, statement-2 is true and statement-2 is correct explanation for statement-1.
B. Staterment-1 is true, statement-2 is true and statement-2 is NOT the correct explanation for statement-1.
C. Statement-1 is true, statement-2 is false.
D. Statement-1 is false, statement-2 is true.

Answer

To analyze the assertion and reason provided in the question, we will break it down step by step.

### Step 1: Understand the Assertion
The assertion states that the first ionization energy of Beryllium (Be) is greater than that of Boron (B).

**Explanation**:
- Beryllium has an atomic number of 4 and its electronic configuration is \(1s^2 2s^2\).
- Boron has an atomic number of 5 and its electronic configuration is \(1s^2 2s^2 2p^1\).
- The first ionization energy is the energy required to remove the outermost electron from an atom.

### Step 2: Compare the Ionization Energies
- For Beryllium, the outermost electrons are in the 2s orbital (2 electrons).
- For Boron, the outermost electrons are in the 2s and 2p orbitals (2 in 2s and 1 in 2p).
- Removing an electron from Beryllium results in a stable configuration (like that of Helium), while removing an electron from Boron leads to a half-filled 2p orbital, which is less stable.

**Conclusion**: The first ionization energy of Beryllium is indeed greater than that of Boron because it is energetically more favorable to remove an electron from Boron.

### Step 3: Understand the Reason
The reason states that the 2p-orbital is lower in energy than the 2s-orbital.

**Explanation**:
- According to the Aufbau principle, the energy levels of orbitals increase in the order of \(1s < 2s < 2p\).
- This means that the 2s orbital is actually lower in energy than the 2p orbital.

### Step 4: Evaluate the Reason
Since the reason provided is incorrect (the 2p orbital is higher in energy than the 2s orbital), we conclude that while the assertion is correct, the reason is not.

### Final Conclusion
- The assertion is **true**: The first ionization energy of Be is greater than that of B.
- The reason is **false**: The 2p orbital is not lower in energy than the 2s orbital.

Thus, the correct answer is that the assertion is true, but the reason is false.

---