Predict the missing component of each reaction. MgO + H2O → Mg(OH)2 2MgO → 2Mg + O2 A. 2Mg + H2O B. 2Mg + O2 C. MgOH + O2 D. MgO + O2
The Correct Answer and Explanation is:
The correct answer is: B. 2Mg + O₂
Explanation
To predict the missing component in a chemical reaction, we analyze the reactants and products and use chemical balancing and reaction types (such as synthesis, decomposition, single replacement, or combustion).
Let’s examine the two given reactions:
- MgO + H₂O → Mg(OH)₂
This is a synthesis reaction (also called a combination reaction), where a metal oxide reacts with water to form a metal hydroxide.
Magnesium oxide (MgO) is a basic oxide, and when it reacts with water, it forms magnesium hydroxide, Mg(OH)₂.
This equation is already complete and balanced. - 2MgO → 2Mg + O₂
This is a decomposition reaction, where a compound breaks down into simpler substances.
Here, magnesium oxide decomposes into elemental magnesium (Mg) and oxygen gas (O₂).
This reaction typically requires electrolysis or a high temperature.
Now, let’s look at the multiple-choice options to find the missing component that can logically fit into this context:
- A. 2Mg + H₂O – This would produce magnesium hydroxide and hydrogen gas, but it’s not related directly to the decomposition of MgO.
- B. 2Mg + O₂ – This is the reverse of the decomposition reaction. When magnesium burns in oxygen, it forms magnesium oxide: 2Mg+O2→2MgO2Mg + O₂ → 2MgO This is a synthesis (combination) reaction, and it is the reverse of the decomposition reaction given earlier.
- C. MgOH + O₂ – MgOH is not a stable or known compound.
- D. MgO + O₂ – This suggests further oxidation, but MgO is already fully oxidized.
Therefore, the correct prediction of the missing component that fits this context is:
✅ B. 2Mg + O₂
This completes the reaction cycle, showing how magnesium forms MgO and how MgO can decompose back into its elements.
