Breaking down of rock in situ refers to the process of the gradual disintegration or decay of rock into smaller pieces without being moved from its original location. This process is known as weathering. Option 1, erosion, is the process of the movement and transportation of weathered materials by agents such as water, wind, and ice. Option 3, mass wasting, is the downhill movement of rock and soil under the influence of gravity, which can be triggered by weathering. Option 4, degradation, refers to the process of wearing down or lowering the level of land surfaces through natural or human-induced processes. It is important to note that while weathering is a key component in the breakdown of rock in situ, erosion, mass wasting, and degradation are all related but distinct processes.