Velocity of water in a river is

Explanation

The velocity of water in a river tends to be more in the middle and less near its banks. This is because the center of the river is farther from the frictional effects of the banks and the riverbed, allowing the water to flow more freely and quickly. Near the banks, the water encounters more friction and obstacles, such as rocks and vegetation, which slow it down. Therefore, Option B is the correct choice. Option A is incorrect because it suggests uniform velocity, which is not the case. Option C is incorrect as it reverses the actual situation, and Option D is incorrect because it implies a simple gradient across the river width, which does not typically occur due to the effects of drag and friction.