Answer: (3) 2 

Solution

Make 3 groups of 3

weigh 2 groups. This will enable you to separate the group that has defective ball. If both are equal than 3rd group has the defective ball.

Now in 2nd turn weight 2 out of the three balls, this will give you the defective ball. If both have same weight, then the 3rd remaining ball is defective.