The elements you mentioned have the following atomic numbers:
- Element A (atomic number 8) is oxygen (O).
- Element B (atomic number 11) is sodium (Na).
- Element C (atomic number 12) is magnesium (Mg).
When oxygen (O) combines with sodium (Na) to form a compound, they combine in a way that satisfies the octet rule and results in a stable compound. Sodium has a +1 charge (Na⁺), and oxygen typically has a -2 charge (O²⁻) when it forms compounds.
To balance the charges, two sodium ions are needed for every one oxide ion:
\[ \text{2 Na}^+ + \text{O}^{2-} \rightarrow \text{Na}_2\text{O} \]
Thus, the formula for the compound formed by the chemical combination of A (oxygen) and B (sodium) is Na₂O (sodium oxide).
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