Painting Surface Area of Sliced Sphere

The surface area of a solid sphere of radius $r$ is $4\pi r^2$. It takes 2 liters to paint $4\pi r^2$.

When sliced into 4 identical pieces (quarter spheres), 4 circular plane surfaces passing through the center are exposed, each of area $\pi r^2$. Total area of these 4 exposed circular faces $= 4 \times \pi r^2 = 4\pi r^2$.

So total surface area of the 4 pieces $= 4\pi r^2 + 4\pi r^2 = 8\pi r^2$.

Since $4\pi r^2$ requires 2 liters, $8\pi r^2$ will require $2 \times 2 = 4$ liters.

Option D is correct.