12, 19, 21, 3, 25, 18, 35, 20, 22, 21, 45, 46, 48, 50, 52, 54, 55,56
Correct Answer: (4) Three
Solution:The number series is as follows.-12, 19, 21, 3, 25, 18, 35, 20, 22, 21, 45, 46, 48, 50, 52, 54,
55,56
required number is 3.
Option (4) is correct.