A Flask Is Charged with 0

Multiple Choice

A flask is charged with 0.124 mol of A and allowed to react to form B according to the reaction A(g) -B(g) . The following data are obtained for [A] as the reaction proceeds:
-The average rate of appearance of B between 20 s and 30 s is mol/s.

A) +5.0 × 10^{- 4}
B) +1.5 × 10^{- 3}
C) - 1.5 × 10^{- 3}
D) - 7.3 × 10^{- 3}
E) +7.3 × 10^{- 3}