19. 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) ΔG° is +1.7 kJ/mol. (B) ΔG° is -1.7 kJ/mol. (C) ΔG° is incalculably large and negative. (D) ΔG° is incalculably large and positive. (E) ΔG° is zero.