Concrete is produced form a mixture of cement, water and small stones. Small amount of gypsum, `CaSO_(4).2H_(2)O` is added in coment production to impove the subsequent hardening of concrete. The elevated temperature during the production of cement may lead to the formation of unwanted hemihydrate `CaSO_(4)(1)/(2)H_(2)O` according to reaction. `CaSO_(4)2H_(2)O(s) rarr CaSO_(4)(1)/(2)H_(2)O(s)+(3)/(2)H_(2)O(g)` The `Delta_(f)H^(Theta) of CaSO_(2).2H_(2)O(s),CaSO_(4)(1)/(2)H_(2)O(s),H_(2)O(g)` are `-2021.0 kJ mol^(-1), -1575.0 kJ mol^(-1)` and `-241.8 kJ mol^(-1)`, respectively. The respective values of their standard entropies are `194.0, 130.0` and `188.0 J K^(-1)mol^(-1)`. The values of `R = 8.314JK^(-1)mol^(-1) = 0.0831L` bar `mol^(-1)K^(-1)`. Answer the following questions on the basis of above information. The equilibrium pressure of water vapour in closed vessel containing `CaSO_(4)2H_(2)O(s),CaSO_(4)(1)/(2)H_(2)O(s)` and `H_(2)O(g)` at `298K` (Antilog `-3.14 = 7.24 xx 10^(-4))` isA. `(17.24 xx 10^(-4))` barB. `(-7.24 xx 10^(-4))^(3)` barC. `(18 xx 10^(-4))^(2//3)`barD. `(7.24 xx 10^(-4))^(2//3)`bar