The first 5 natural numbers are: 1, 2, 3, 4, 5

Mean = (1 + 2 + 3 + 4 + 5)/5 = 15/5 = 3

Now, varience = {∑(x_i )² }/n - (Mean)²                  {1 ≤ i ≤ 5}

                   = (1² + 2² + 3² + 4² + 5² )/5 - 3² 

                   = (1 + 4 + 9 + 16 + 25)/5 - 9

                   = 55/5 - 9

                   = 11 - 9

                   = 2

So, the varience of the first 5 natural number is 2

Shortcut Method:

The varience of the first n natural number = (n² - 1)/12

Here, n = 5

So, varience = (5² - 1)/12

                 = (25 - 1)/12

                 = 24/12

                 = 2