A Concentration-Time Study of the Gas Phase Reaction 2 A₃

A concentration-time study of the gas phase reaction 2 A₃ → 3 A₂ produced the data in the table below. Time (s) [A₃] (M) [A₂] (M)
0 4.00 × 10^-4 0
10 2.00 × 10^-4 3.00 × 10^-4
20 1.00 × 10^-4 4.50 × 10^-4
30 5.00 × 10^-5 ?
What is the average rate of decomposition of A₃ in the time interval 20-30 seconds?

A) 4.00 × 10^-4 M/s
B) 3.50 × 10^-5 M/s
C) 5.00 × 10^-6 M/s
D) 4.00 × 10^-6 M/s