A box contain 3 red balls, 2 white balls and 1 green ball. What is the sample space of the experiment?

The box contains red balls, white balls, and green balls.

When you draw a single ball from the box, it can be either red, white, or green. The number of balls of each color affects the probability of drawing that color, but not the set of possible outcomes themselves.

The sample space is the set of all possible distinct outcomes of an experiment. In this case, the experiment is drawing one ball.

The sample space of the experiment is $\boxed{\{ \text{Red, White, Green} \}}$.