Which of the choices is the standard deviation of the sample shown here?

19, 20, 21, 22, 23

a.2.5
b.21
c. square root of 2.5
d.2
e. square root of 2

Mean = (19 + 20 + 21 + 22 + 23)/5 = 105/5 = 21
x    x - mean   (x - mean)^2
19     -2                4
20     -1                1
21      0                0
22      1                1
23      2                4
               Sum = 10

Standard deviation = sqrt(sum(x - mean)^2 /n) = sqrt(10/5) = sqrt(2)