(\text{If whole surface area of a sphere is } 100\pi \text{, then radius will be})

Surface area of a sphere = 4πr². Given 4πr² = 100π. Dividing both sides by 4π: r² = 25. Taking square root: r = 5. So the radius is 5 units. Remember to divide the total surface area by 4π first before taking the square root. Options like 4, 4.5, and 7 would give surface areas of 64π, 81π, and 196π respectively, none of which equal 100π.