Option 1 states that the reaction of calcium with sulphuric acid is not feasible at room temperature. This option is incorrect. The reaction between calcium and sulphuric acid is indeed feasible, but it stops after a short while for a different reason.

Option 2 states that the formed calcium sulphate is insoluble in water and covers the calcium metal, preventing it from reacting any further. This option is the correct answer. When calcium reacts with sulphuric acid, calcium sulphate is formed. Calcium sulphate is a white solid that is insoluble in water. As it forms, it coats the calcium metal surface, creating a layer of calcium sulphate. This layer acts as a barrier and prevents any further reaction between the calcium metal and sulphuric acid.

Option 3 states that formed calcium sulphate requires two molecules of water to crystallize as gypsum. This option is not directly related to why the reaction stops and can be considered irrelevant to the question.

Option 4 states that formed calcium sulphate is unstable. This option is also not the reason why the reaction stops. Calcium sulphate is indeed a stable compound and does not contribute to the reaction stopping.

In summary, Option 2 is the correct answer as it explains that the formation of insoluble