The gas evolved on heating `CaF_(2) and SiO_(2)` with concentrated `H_(2)SO_(4)`, on hydrolysis gives a white gelatinous precipitate.
The precipitate is :

Options

A. hydrofluorosilicic acid
B. silica gel
C. silicic acid
D. calciumfuorosilicate

Explanation

To solve the question, we need to analyze the reactions that occur when calcium fluoride (CaF₂) and silicon dioxide (SiO₂) are heated with concentrated sulfuric acid (H₂SO₄) and then undergo hydrolysis.

### Step-by-Step Solution:

1. **Identify the Initial Reaction**:
When calcium fluoride (CaF₂) is heated with concentrated sulfuric acid (H₂SO₄), it reacts to produce hydrogen fluoride (HF) and calcium sulfate (CaSO₄).
\[ \text{CaF}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{HF} + \text{CaSO}_4 \]

2. **Identify the Second Reaction**:
The hydrogen fluoride gas produced can then react with silicon dioxide (SiO₂). This reaction forms silicon tetrafluoride (SiF₄) and water (H₂O).
\[ \text{HF} + \text{SiO}_2 \rightarrow \text{SiF}_4 + \text{H}_2\text{O} \]

3. **Hydrolysis of Silicon Tetrafluoride**:
The silicon tetrafluoride (SiF₄) gas can then undergo hydrolysis when it comes into contact with water. This reaction produces hydrofluorosilicic acid (H₂SiF₆) and silica (SiO₂), which is a white gelatinous precipitate.
\[ \text{SiF}_4 + 2 \text{H}_2\text{O} \rightarrow \text{H}_2\text{SiF}_6 + \text{SiO}_2 \]

4. **Conclusion**:
The white gelatinous precipitate formed during hydrolysis is silica (SiO₂). Therefore, the answer to the question is that the precipitate is **silica**.

### Final Answer:
The white gelatinous precipitate is **silica (SiO₂)**.