How many of the following show variable oxidation states in their compounds?
Sc,Cr,Cu,Zn,Fe,Hg,La

Answer

To determine how many of the given elements show variable oxidation states in their compounds, we will analyze each element one by one.

1. **Scandium (Sc)**:
- Atomic Number: 21
- Electronic Configuration: [Ar] 3d¹ 4s²
- Oxidation States: Scandium exhibits +2 and +3 oxidation states.
- **Conclusion**: Scandium shows variable oxidation states.

2. **Chromium (Cr)**:
- Atomic Number: 24
- Electronic Configuration: [Ar] 3d⁴ 4s²
- Oxidation States: Chromium can exhibit +2, +3, +4, +5, and +6 oxidation states.
- **Conclusion**: Chromium shows variable oxidation states.

3. **Copper (Cu)**:
- Atomic Number: 29
- Electronic Configuration: [Ar] 3d¹⁰ 4s¹
- Oxidation States: Copper shows +1 and +2 oxidation states.
- **Conclusion**: Copper shows variable oxidation states.

4. **Zinc (Zn)**:
- Atomic Number: 30
- Electronic Configuration: [Ar] 3d¹⁰ 4s²
- Oxidation States: Zinc primarily shows +2 oxidation state.
- **Conclusion**: Zinc does not show variable oxidation states.

5. **Iron (Fe)**:
- Atomic Number: 26
- Electronic Configuration: [Ar] 3d⁶ 4s²
- Oxidation States: Iron can exhibit +2, +3, +4, +5, and +6 oxidation states.
- **Conclusion**: Iron shows variable oxidation states.

6. **Mercury (Hg)**:
- Atomic Number: 80
- Electronic Configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s²
- Oxidation States: Mercury shows +1 and +2 oxidation states.
- **Conclusion**: Mercury shows variable oxidation states.

7. **Lanthanum (La)**:
- Atomic Number: 57
- Electronic Configuration: [Xe] 4f¹ 5d¹ 6s²
- Oxidation States: Lanthanum primarily shows +3 oxidation state.
- **Conclusion**: Lanthanum does not show variable oxidation states.

Now, we will summarize the findings:
- Elements showing variable oxidation states: Scandium, Chromium, Copper, Iron, Mercury.
- Elements not showing variable oxidation states: Zinc, Lanthanum.

**Total Elements with Variable Oxidation States**: 5 (Sc, Cr, Cu, Fe, Hg)

### Final Answer:
**5 elements show variable oxidation states in their compounds.**

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