Concept:
The potential energy stored in a spring is given by the formula:
\[
U = \frac{1}{2}kx^2
\]
where
\(k\) = spring constant and
\(x\) = displacement from equilibrium.
Step 1: Substitute the given values.
\[
k = 100\,\text{N/m}, \quad x = 0.2\,\text{m}
\]
\[
U = \frac{1}{2}\times100\times(0.2)^2
\]
Step 2: Compute the value.
\[
(0.2)^2 = 0.04
\]
\[
U = \frac{1}{2}\times100\times0.04
\]
\[
U = 2\,\text{J}
\]
Thus, the potential energy stored in the spring is
\[
\boxed{2\,\text{J}}
\]