**Deducing the Chemical Formula of Magnesium Oxide**

To deduce the chemical formula of magnesium oxide, we need to understand the nature of the elements involved and their combining capacities. Magnesium (Mg) is an alkaline earth metal, and oxygen (O) is a non-metal. Both elements have specific valencies or combining capacities that determine how they bond with other elements.

**Step 1: Identify the Valencies of the Elements**
The valency of magnesium is +2, meaning it tends to lose two electrons to achieve a stable electron configuration. On the other hand, oxygen has a valency of -2, indicating its tendency to gain two electrons to attain stability.

**Step 2: Determine the Ratio**
To form a stable compound, the combining capacities of the two elements need to balance. Since magnesium has a valency of +2 and oxygen has a valency of -2, we need two oxygen atoms to bond with one magnesium atom to maintain charge neutrality. This ratio will ensure that the total positive charge from the magnesium is balanced by the total negative charge from the oxygen.

**Step 3: Write the Chemical Formula**
The chemical formula of magnesium oxide can be derived from the ratio determined in the previous step.

- The symbol of magnesium is Mg.
- The symbol of oxygen is O.

Since we need two oxygen atoms to bond with one magnesium atom, we write the chemical formula as MgO.

**Step 4: Balance the Charges**
Finally, it is important to note that the overall compound must be electrically neutral. In the case of magnesium oxide, magnesium has a charge of +2 and oxygen has a charge of -2. The charges balance each other out, resulting in a neutral compound.

In summary, the chemical formula of magnesium oxide is MgO. By understanding the valencies and combining capacities of magnesium and oxygen, we can determine the ratio of atoms and write the correct formula.

Step 1 : Write the symbols of the radicals. Step 2 : Write the valency below the respective radical. Step 3 : Cross-multiply symbols of radicals with their respective valency. Step 4 : Write down the chemical formula of the compound.