Surface Area of Cut Sphere

Surface area of full sphere = $4\pi r^2$, requiring 2 liters. Cutting into 4 identical pieces (quarter spheres) creates 4 internal circular flat surfaces of area $\pi r^2$ each, i.e., an additional $4\pi r^2$ surface area. Total new surface area = $4\pi r^2 + 4\pi r^2 = 8\pi r^2$, which is double the original. Thus, paint required = $2 \times 2 = 4.0$ liters.