Which of the following has a tetragonal crystal system?

Calcium sulphate

The correct answer is option 4. Calcium sulphate.

The crystal system of a substance is determined by the regular arrangement of atoms or molecules in its crystalline structure. Among the options provided, the substance with a tetragonal crystal system is Calcium sulphate

Calcium sulfate, commonly known as gypsum, exhibits a tetragonal crystal system. In its natural form, gypsum crystals often appear as prismatic or tabular crystals with well-defined faces.