A square pond has 2m sides and is 1m deep. If it is to be enlarged, the depth remaining the same, into a circular pond with the diagonal of the square as diameter as shown in the figure, then what would be the volume of earth to be removed?

The square pond has side 2 m and depth 1 m; its diagonal is 2√2 m and is taken as the diameter of the circular pond, so the circular pond’s radius is √2 m. The original pond’s volume = area × depth = (2×2)×1 = 4 m^3. The circular pond’s volume is V = πr^2h = π(√2)^2×1 = 2π m^3, using the cylinder volume formula. The volume of earth to be removed equals the extra volume: 2π − 4 cubic metres. Hence the correct choice is option 1: (2π − 4) m^3.