Final answer:
2:1 clays are made up of a structural arrangement consisting of tetrahedral, octahedral, and tetrahedral sheets, with an octahedral sheet sandwiched between two tetrahedral sheets. The correct option is 1.
Step-by-step explanation:
2:1 Clays are composed of layers of silica tetrahedra and metal oxides. Specifically, they consist of one octahedral sheet sandwiched between two tetrahedral sheets. Thus, the correct structural sequence is tetrahedral, octahedral, tetrahedral sheets.
In these sheets, the silica tetrahedra, which are a combination of one silicon atom and four oxygen atoms, form a two-dimensional network with a net charge. The octahedral sheet consists of metal cations such as aluminum or magnesium surrounded by oxygen or hydroxyl groups.
These layers are held together by various ionic and van der Waals forces, with various cations like potassium or sodium ions found in the interlayer spaces.