Arrange from smallest to largest 0.2 , 0.06, 0.602, 0.026, 0.21

0.026, 0.06, 0.21, 0.2, 0.602

The population size of the above data is 8, that is N=8
The mean (average) = (12 +10+ 11.5 +11.5 +12 +9 +9 +11)/8
                                 = 10.75
Standard deviation is the square root of variance, it is one of the measures of central dispersion, that is a measure of by how much the values in the data set are likely to differ from the mean. 
In this case, Standard deviation, s= √(∑(x-m)²)/(n-1)
                                                  = 1.172 
Thus, best approximation of the standard deviation is 1.17