In following number series, two terms have been put within brackets. Choose the appropriate option - Look at this series: 2, 6, 18, 54, . . .What number should come next?

Answer: C. 162

This is a simple multiplication series.
Each number is 3 times more than the previous number.
The series is 2, 6, 18, 54, . . .
Rule = (1st number x 3 = 2nd number) (2nd number x 3 = 3rd number)....
Now (2) (2 x 3 = 6), (6 x 3 = 18), (18 x 3 = 54) (54 x 3 = 162)...
So the answer is c = 162.