G° for the conversion of glycerol-3-phosphate to glycerol + Pi is -2.2 kcal/mole. Thus, you
can conclude that...
a. this reaction may or may not occur spontaneously, depending on the actual concentrations of reactants and products.
b. this reaction is so strongly favorable that it could be coupled to drive an otherwise unfavorable cell reaction.
c. this reaction will occur spontaneously.
d. this reaction will only occur spontaneously if it is coupled to another reaction that has a more favorable G°.