The correct answer is A. 5 to 10 cm/sec.
A sedimentation tank is a type of water treatment plant that uses gravity to separate suspended solids from water. The velocity of flow of water in a sedimentation tank is typically in the range of 5 to 10 cm/sec. This is slow enough to allow the suspended solids to settle out of the water, but fast enough to prevent the water from becoming stagnant.
Option B is incorrect because the velocity of flow of water in a sedimentation tank is typically much lower than 15 to 30 cm/sec. Option C is incorrect because the velocity of flow of water in a sedimentation tank is typically much higher than 15 to 30 cm/minute. Option D is incorrect because the velocity of flow of water in a sedimentation tank is typically much higher than 15 to 30 cm/hour.