1. Take 3 bags and compare it with another 3 bags, if they are equal, then take remaining two bags and compare. Total wieghtings = 2.
2. If in step one, if 3 bags are not equal to another three bags. Then take the heavier 3 bag group and pick any 2 bags and compare , if they are same, then 3rd bag is heavy bag.If not, the we will get heavy bag anyway.
So, in either case only 2 wieghtings is required. Hence , Answer is A.