`Mg overset("dry. Air"//Delta)toA+B`

Options

A. A & B are MgO & `MgO_(2)`
B. A & B are `MgO_(2)& Mg(OH)_(2)`
C. A+B are `MgO+Mg_(3)N_(2)`
D. A & B are `MgO_(2) & Mg_(3)N_(2)`

Answer

To solve the question regarding the reaction of magnesium (Mg) with dry air when heated, we need to identify the compounds formed during this reaction.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- When magnesium is heated in dry air, it reacts with the gases present in the air, primarily oxygen and nitrogen.

2. **Identifying the Products**:
- Magnesium reacts with oxygen (O₂) to form magnesium oxide (MgO).
- Magnesium can also react with nitrogen (N₂) to form magnesium nitride (Mg₃N₂).

3. **Writing the Reaction**:
- The overall reaction can be represented as:
\[ 3Mg + O_2 \rightarrow 3MgO \quad \text{(Formation of magnesium oxide)} \]
\[ 3Mg + N_2 \rightarrow Mg_3N_2 \quad \text{(Formation of magnesium nitride)} \]

4. **Identifying Compounds A and B**:
- From the reactions above, we can conclude that:
- Compound A is magnesium oxide (MgO).
- Compound B is magnesium nitride (Mg₃N₂).

5. **Final Answer**:
- Therefore, the compounds formed when magnesium reacts with dry air upon heating are:
- A = MgO (magnesium oxide)
- B = Mg₃N₂ (magnesium nitride)