The increasing order of the first ionisation enthalpies of the elements`B,P,S` and `F` (lowest first) is:

Options

A. `B lt S lt P lt F`
B. `F lt S lt P lt B`
C. `P lt S lt B lt F `
D. `B lt P lt S lt F`

Answer

To determine the increasing order of the first ionization enthalpies of the elements Boron (B), Phosphorus (P), Sulfur (S), and Fluorine (F), we need to analyze the factors that affect ionization energy.

### Step-by-Step Solution:

1. **Understanding Ionization Energy**:
- Ionization energy is the energy required to remove an electron from an isolated gaseous atom.
- It generally increases across a period (from left to right) and decreases down a group (from top to bottom) in the periodic table.

2. **Identifying the Elements**:
- The elements in question are:
- Boron (B) - Group 13
- Phosphorus (P) - Group 15
- Sulfur (S) - Group 16
- Fluorine (F) - Group 17

3. **Comparing Ionization Energies**:
- **Fluorine (F)**: Being in Group 17, it has the highest ionization energy due to its high electronegativity and small atomic size.
- **Boron (B)**: It is in Group 13 and has the lowest ionization energy among the four elements due to its larger atomic size compared to F and the fact that it has fewer protons attracting the outermost electron.
- **Phosphorus (P)**: It has a half-filled p-orbital configuration (3s² 3p³), which provides extra stability. Therefore, it has a higher ionization energy than sulfur.
- **Sulfur (S)**: It has a higher ionization energy than phosphorus but lower than fluorine.

4. **Arranging in Increasing Order**:
- Based on the above analysis, we can arrange the elements in increasing order of their first ionization enthalpies:
- Boron (B) < Phosphorus (P) < Sulfur (S) < Fluorine (F)

5. **Final Answer**:
- The increasing order of the first ionization enthalpies of B, P, S, and F is: **B < P < S < F**.