The volume of a sphere is $V = \frac{4}{3}\pi r^3$. The percentage error in $V$ is $\frac{\Delta V}{V} \times 100 = 3 \left( \frac{\Delta r}{r} \times 100 \right)$. Given the percentage error in $r$ is $2\%$, the percentage error in $V = 3 \times 2\% = 6\%$. Constants like $4/3$ and $\pi$ do not contribute to the error.