Letthe number of bacteria in a certain food be x.
Since, they double in every second, the series is:
x,2x,2(2x),2(2(2(x))),…
i.e x,2x,4x,8x,…
t2−t1=2x−x=x
t3−t2=4x−2x=2x
t4−t3=8x−4x=4x
Since the difference between each successive term is not same, the list does not form an AP.