Which of the following does not exhibit the periodicity in properties of the elements?

Options

A. ionisation energy
B. N/P ratio
C. electronegativity
D. atomic radius

Explanation

To determine which of the following options does not exhibit periodicity in the properties of elements, we need to analyze the periodic trends of each property mentioned.

### Step-by-Step Solution:

1. **Understanding Periodicity**:
- Periodicity refers to the trends and patterns observed in the properties of elements as you move across a period or down a group in the periodic table. Properties such as ionization energy, electronegativity, and atomic radius show regular trends.

2. **Analyzing Ionization Energy**:
- Ionization energy generally increases from left to right across a period due to increasing nuclear charge and decreases from top to bottom in a group due to increased distance from the nucleus and electron shielding.
- **Conclusion**: Ionization energy exhibits periodicity.

3. **Analyzing Electronegativity**:
- Electronegativity also increases from left to right across a period and decreases from top to bottom in a group, similar to ionization energy.
- **Conclusion**: Electronegativity exhibits periodicity.

4. **Analyzing Atomic Radius**:
- Atomic radius decreases from left to right across a period due to increased nuclear charge pulling electrons closer to the nucleus and increases from top to bottom in a group due to the addition of electron shells.
- **Conclusion**: Atomic radius exhibits periodicity.

5. **Analyzing n/p Ratio**:
- The n/p ratio (neutron to proton ratio) is influenced by nuclear stability and does not show a regular trend across the periodic table. It can vary significantly without following a predictable pattern.
- **Conclusion**: The n/p ratio does not exhibit periodicity.

### Final Answer:
The property that does not exhibit periodicity in the properties of elements is the **n/p ratio**.

---