Which of the following is potash alum ?

$K_2SO_4Al_2(SO_4)_3.24H_2O$

The correct answer is option 2. $K_2SO_4Al_2(SO_4)_3.24H_2O$.

Potash alum, also known as potassium aluminum sulfate, has the chemical formula \(K_2SO_4Al_2(SO_4)_3.24H_2O\). Let's break down this formula:

1. \(K_2SO_4\):  This represents the potassium sulfate component.

2. \(Al_2(SO_4)_3\): This represents the aluminum sulfate component.

3. \(24H_2O\): This indicates the presence of 24 water molecules (water of crystallization).

The combination of these elements results in potash alum. The potassium sulfate and aluminum sulfate components contribute to the overall chemical structure, and the 24 water molecules are part of the crystal structure of the compound.

Potash alum is commonly used in various applications, including as a mordant in dyeing fabrics, in water purification processes, and in certain traditional remedies. The water molecules in its structure are part of the crystalline structure and can be removed by heating, resulting in the anhydrous form of alum.