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. Calciumfluorosilicate

Explanation

To solve the problem, let's break down the steps involved in the reaction of calcium fluoride (CaF₂) and silicon dioxide (SiO₂) with concentrated sulfuric acid (H₂SO₄), and determine the precipitate formed upon hydrolysis.

### Step 1: Identify the Reactants and Conditions
We are given:
- Calcium fluoride (CaF₂)
- Silicon dioxide (SiO₂)
- Concentrated sulfuric acid (H₂SO₄)

### Step 2: Write the Reaction
When CaF₂ and SiO₂ are heated with concentrated H₂SO₄, the following reaction occurs:

\[ \text{CaF}_2 + \text{SiO}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{SiF}_4 + \text{CaSO}_4 + \text{H}_2\text{O} \]

In this reaction:
- Silicon tetrafluoride (SiF₄) is produced.
- Calcium sulfate (CaSO₄) and water (H₂O) are also formed.

### Step 3: Hydrolysis of the Products
Upon hydrolysis of the products, particularly SiF₄, it reacts with water to form silicic acid (H₂SiO₃) and hydrofluoric acid (HF):

\[ \text{SiF}_4 + 2\text{H}_2\text{O} \rightarrow \text{H}_2\text{SiO}_3 + 4\text{HF} \]

### Step 4: Formation of the Precipitate
Silicic acid (H₂SiO₃) is a gel-like substance that forms a white gelatinous precipitate when it is produced. This is the precipitate we are looking for.

### Conclusion
The white gelatinous precipitate formed upon hydrolysis is **silicic acid (H₂SiO₃)**.

### Final Answer
The precipitate is: **Silicic acid (H₂SiO₃)**.