Which of the following properties of isotopes of an element is different?

Options

A. First ionisation enthalpy
B. Effective nuclear charge
C. Electron affinity
D. Melting point and Boiling point

Explanation

To determine which property of isotopes of an element is different, we need to analyze the characteristics of isotopes and the properties listed in the options.

### Step-by-Step Solution:

1. **Understanding Isotopes**:
- Isotopes are atoms of the same element that have the same atomic number but different mass numbers. This means they have the same number of protons (and electrons) but a different number of neutrons.

2. **Identifying Properties**:
- The question provides four properties to consider:
- A) Ionization enthalpy
- B) Effective nuclear charge
- C) Electron affinity
- D) Melting point and boiling point

3. **Chemical vs. Physical Properties**:
- Isotopes have the same chemical properties because they have the same number of electrons and the same atomic structure. Therefore, properties like ionization enthalpy, effective nuclear charge, and electron affinity will be the same for isotopes.
- However, isotopes can differ in physical properties due to their different mass numbers. This includes properties like melting point and boiling point.

4. **Analyzing the Options**:
- **Ionization Enthalpy**: Same for isotopes (chemical property).
- **Effective Nuclear Charge**: Same for isotopes (chemical property).
- **Electron Affinity**: Same for isotopes (chemical property).
- **Melting Point and Boiling Point**: Different for isotopes (physical property).

5. **Conclusion**:
- The property that differs among isotopes of an element is the melting point and boiling point. Therefore, the correct answer is option D.

### Final Answer:
**D) Melting point and boiling point**

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