Write the formulae of different compounds formed among the given elements.
`{:("Element","Combining power"),("Ca",2),("O",2),("Fe",3),("S",2),("Na",1):}`

Explanation

To write the formulae of different compounds formed among the given elements, we need to consider the combining power (valency) of each element. Let's analyze the elements and their combining powers:

1. **Calcium (Ca)**: Combining power = 2
2. **Oxygen (O)**: Combining power = 2
3. **Iron (Fe)**: Combining power = 3
4. **Sulfur (S)**: Combining power = 2
5. **Sodium (Na)**: Combining power = 1

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