Answer
The force is attractive when $~~r \gt 0.2~nm$
Work Step by Step
The force $F$ is attractive when $F \lt 0$
We can write an expression for $F$:
$F = -\frac{dU}{dx}$
For the values of $r$ such that $r \gt 0.2~nm$, the slope of the $U$ versus $r$ curve is positive. Then the value of $\frac{dU}{dx}$ is positive, and the force $F$ is negative.
The force is attractive when $~~r \gt 0.2~nm$
