Correct Answer - Option 2 : 11 minutes
The height of a pole = 21 meters
A monkey covers distance in 1 minute = 6 meters
Net distance travelled by monkey in 2 min = 3 meters
In 10 min. distance travelled (climbed) = 15 meters
As, it is given in the question that in first minute it climbed 6 meters and in other minute it slips down 3 meters
And this happens alternately.
So monkey will travel remaining 6 meters in next minute.
∴ Total time taken is (10 + 1) = 11 minute.