The riverbank is weakest where the river turns. This is because water

The correct answer is Option 2. When a river reaches a bend or meander, the momentum of the moving water carries it toward the outer bank. This results in the water effectively "colliding" with or bouncing off the bank, exerting significant centrifugal force and extra hydraulic pressure.

This process makes Option 2 correct because:

• Lateral Erosion: The extra pressure accelerates undercuting and bank failure on the outer curve (cut bank).
• Flow Dynamics: While water velocity is indeed higher on the outer bank (contradicting Option 3's vagueness), it is the physical impact and pressure of the redirected mass of water that directly weakens the structural integrity of the bank.
• Deposition: Conversely, the inner bank experiences lower velocity, leading to sediment deposition (point bars), making it stable rather than weak, which invalidates Option 1.

In Geomorphology, this constant pressure on the outer bank is the primary driver of meander migration and riverbank instability.