Given the reaction at 101.3 kilopascals and 298 k: hydrogen gas + iodine gas → hydrogen iodide gas
this reaction is classified as
(1) endothermic, because heat is absorbed
(2) endothermic, because heat is released
(3) exothermic, because heat is absorbed
(4) exothermic, because heat is released

the correct answer is "exothermic, because heat is released."

explanation:

in an endothermic process heat is absorbed by the system and in an exothermic process heat is released by the system.

the heat of formation of hydrogen iodide is -9.4 kj/mol. hence the formation of hydrogen iodide from hydrogen and iodine is an exothermic process. heat released is shown by a negative value of enthalpy.

the formula would be mgso4

mgso[subscript]4