A certain element is forms a solid oxide which dissolves in water to form an acidic solution. The element is

Options

A. Na
B. Mg
C. S
D. P

Explanation

To determine which element forms a solid oxide that dissolves in water to produce an acidic solution, we can analyze the properties of the elements in question.

### Step-by-Step Solution:

1. **Identify the Elements**: The elements we need to consider are sodium (Na), magnesium (Mg), sulfur (S), and phosphorus (P).

2. **Examine Sodium (Na)**:
- Sodium forms sodium oxide (Na2O).
- When Na2O dissolves in water, it produces sodium hydroxide (NaOH), which is a basic solution.
- **Conclusion**: Sodium does not meet the criteria as it produces a basic solution.

3. **Examine Magnesium (Mg)**:
- Magnesium forms magnesium oxide (MgO).
- When MgO dissolves in water, it produces magnesium hydroxide (Mg(OH)2), which is also a basic solution.
- **Conclusion**: Magnesium does not meet the criteria as it produces a basic solution.

4. **Examine Sulfur (S)**:
- Sulfur can form sulfur dioxide (SO2) and sulfur trioxide (SO3), which are gases.
- Since the question specifies a solid oxide, sulfur does not meet the criteria.
- **Conclusion**: Sulfur is not the correct element.

5. **Examine Phosphorus (P)**:
- Phosphorus can form solid oxides such as tetraphosphorus decoxide (P4O10) and tetraphosphorus hexoxide (P4O6).
- When P4O10 dissolves in water, it forms phosphoric acid (H3PO4), which is an acidic solution.
- When P4O6 dissolves in water, it forms phosphorous acid (H3PO3), which is also acidic.
- **Conclusion**: Phosphorus meets the criteria as it forms a solid oxide that dissolves in water to produce an acidic solution.

6. **Final Answer**: The element that forms a solid oxide which dissolves in water to form an acidic solution is **Phosphorus (P)**.