18. When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme phosphohexose isomerase, the final mixture contains twice as much glucose 6-phosphate as fructose 6-phosphate. Which one of the following statements is most nearly correct, when applied to the reaction below? (R = 8.315 J/mol.K and T = 298 K)Glucose 6-phosphate

fructose 6-phosphate
(A)

is +1.7 kJ/mol.
(B) 

 is-1.7 kJ/mol. 
(C) 

is incalculably large and negative.
(D)

 is incalculably large and positive.
(E) 

is zero.