In what minimum volume of water can
1 g of gypsum be dissolved?

If it's in water solution, not much you can do about it, as gypsum does dissolve in water. You could run it through a water softening filter, but those are usually hooked into your water line. Boiling the water may precipitate some out as anhydrite, but I think there will still be some gypsum left in solution.

hoped that helped

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.