ANS:C - synthetic zeolites crystals/metal alumino-silicates.

Synthetic zeolites are crystalline, microporous materials with a framework structure consisting of interconnected tetrahedra of oxygen atoms and metal cations, typically aluminum and silicon. These materials are often referred to as metal alumino-silicates because they contain aluminum and silicon in their framework. Here's an explanation of synthetic zeolites and metal alumino-silicates:

1. Composition: Synthetic zeolites are composed of a three-dimensional framework of SiO4 and AlO4 tetrahedra linked by oxygen atoms. Aluminum atoms replace some of the silicon atoms in the tetrahedral structure, leading to a negative charge in the framework. To balance this charge, cations such as sodium (Na+), potassium (K+), or calcium (Ca2+) are located within the pores of the structure.
2. Porous Structure: The crystalline structure of synthetic zeolites contains regularly spaced micropores and channels of uniform size, typically in the range of a few angstroms to several nanometers. These micropores give zeolites their unique molecular sieving properties, allowing them to selectively adsorb molecules based on size and polarity.
3. Applications: Synthetic zeolites are widely used in various industrial applications due to their unique properties. They are commonly used as adsorbents, catalysts, ion exchangers, and molecular sieves in processes such as gas separation, purification, dehydration, and catalytic reactions. For example, zeolites are used in detergent formulations for water softening, in petrochemical refining for adsorption and separation of hydrocarbons, and in environmental applications for water and air purification.
4. Tailored Properties: The properties of synthetic zeolites can be tailored by adjusting the synthesis conditions, such as the composition of the reaction mixture, temperature, pressure, and duration of crystallization. This allows for the synthesis of zeolites with specific pore sizes, surface areas, and chemical compositions tailored to particular applications.
5. Advantages: Synthetic zeolites offer several advantages over natural zeolites, including higher purity, greater uniformity in properties, and the ability to produce zeolites with desired characteristics for specific applications. They are also more readily available in large quantities and can be produced with controlled compositions and structures.