To determine how many of the given elements exclusively occur in a combined state, we will analyze each element listed: Gold, Iron, Zinc, Aluminium, Platinum, Sodium, and Magnesium.
### Step-by-Step Solution:
1. **Identify the Elements**: The elements we need to analyze are:
- Gold (Au)
- Iron (Fe)
- Zinc (Zn)
- Aluminium (Al)
- Platinum (Pt)
- Sodium (Na)
- Magnesium (Mg)
2. **Understand the Forms of Elements**: Elements can exist in two forms:
- **Native (Free) State**: Elements that occur in their pure form without combining with other elements. These typically have low reactivity and do not readily combine with air or moisture.
- **Combined State**: Elements that are found in nature combined with other elements, often in the form of ores, oxides, sulfides, etc.
3. **Analyze Each Element**:
- **Gold (Au)**: Occurs in the native state. It is found in its pure form in nature.
- **Iron (Fe)**: Primarily found in combined states, such as in iron oxides (e.g., Fe2O3).
- **Zinc (Zn)**: Typically found in combined states, such as in zinc oxide (ZnO) and zinc sulfide (ZnS).
- **Aluminium (Al)**: Found in combined states, mainly in bauxite (Al2O3).
- **Platinum (Pt)**: Occurs in the native state, similar to gold, as it is resistant to corrosion and oxidation.
- **Sodium (Na)**: Found in combined states, primarily in sodium chloride (NaCl).
- **Magnesium (Mg)**: Typically found in combined states, such as in magnesium chloride (MgCl2).
4. **Count the Elements in Combined State**:
- From the analysis:
- Elements in native state: Gold (Au), Platinum (Pt)
- Elements in combined state: Iron (Fe), Zinc (Zn), Aluminium (Al), Sodium (Na), Magnesium (Mg)
Therefore, the elements that exclusively occur in the combined state are Iron, Zinc, Aluminium, Sodium, and Magnesium.
5. **Conclusion**: There are **5 elements** (Iron, Zinc, Aluminium, Sodium, and Magnesium) that exclusively occur in the combined state.
### Final Answer:
**5 elements exclusively occur in the combined state.**
---
