Which fo the following statements about zeolites is not correct ?

Options

A. Zeolites are open structures of silica in which trivalent aluminum is substituted by a fraction of silicon atoms
B. Shape selectivity fo zeolites depends upon porous structures of the catalyst
C. Zeolites are synthetic microporous aluminosilicates which do not exist naturally
D. Zeolites are aluminosilicates having three dimensional network

Answer

To determine which statement about zeolites is not correct, we will analyze each statement provided.

### Step-by-Step Solution:

1. **Understanding Zeolites**:
- Zeolites are microporous aluminosilicate minerals with an open 3D framework. They can occur naturally or be synthesized industrially.

2. **Analyzing the Statements**:
- **Statement 1**: "Zeolites are an open structure of silica in which trivalent aluminum is substituted by a fraction of silicon atom."
- This statement is correct. Zeolites have a framework where silicon (Si) and aluminum (Al) atoms are arranged in a tetrahedral structure, with SiO4 and AlO4 units.

- **Statement 2**: "Shape selectivity of zeolites depends upon the porous structure of the catalyst."
- This statement is also correct. The shape selectivity refers to the ability of zeolites to allow certain molecules to enter their pores based on size and shape, which is a function of their porous structure.

- **Statement 3**: "Zeolites are synthetic microporous aluminosilicates, which do not exist naturally."
- This statement is incorrect. While zeolites can be synthesized, they also occur naturally in volcanic rocks and other geological formations.

- **Statement 4**: "Zeolites are aluminosilicates having a three-dimensional network."
- This statement is correct. Zeolites indeed have a three-dimensional framework structure.

3. **Conclusion**:
- The statement that is not correct about zeolites is **Statement 3**: "Zeolites are synthetic microporous aluminosilicates, which do not exist naturally."

### Final Answer:
The incorrect statement about zeolites is Statement 3.

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