Magnesium reacts with______to form magnesium oxide.

Options

A. water
B. cold water
C. steam
D. dil.HCl

Answer

To answer the question "Magnesium reacts with______to form magnesium oxide," we will analyze the options provided and determine the correct answer step by step.

### Step-by-Step Solution:

1. **Understanding the Reaction**: Magnesium (Mg) is a metal that can react with various substances. We need to identify which of the given options leads to the formation of magnesium oxide (MgO).

2. **Analyzing the Options**:
- **Option A: Water** - Magnesium does not react with liquid water under normal conditions.
- **Option B: Cold Water** - Similar to option A, magnesium does not react with cold water.
- **Option C: Steam** - Magnesium reacts with steam (water vapor) to form magnesium oxide and hydrogen gas.
- **Option D: Diluted HCl** - While magnesium can react with hydrochloric acid, it does not produce magnesium oxide directly.

3. **Identifying the Correct Reaction**: The relevant reaction for magnesium with steam is:
\[ Mg + H_2O (steam) \rightarrow MgO + H_2 \]
In this reaction, magnesium reacts with steam to produce magnesium oxide and hydrogen gas.

4. **Conclusion**: From the analysis, the correct answer is that magnesium reacts with steam to form magnesium oxide.

### Final Answer:
Magnesium reacts with **steam** to form magnesium oxide.