Which factor can help form a pitted or weakened layer on rock surface?

Correct answer: Uneven dissolution and alteration of minerals

A rock surface can become pitted or weak when its minerals do not respond to weathering at the same rate. Some minerals may dissolve relatively quickly, while others may alter more slowly or resist dissolution. This uneven removal leaves small hollows, rough patches, and zones of weakness on the surface. Water, oxygen, acids, and changes in temperature can influence these reactions, but the important idea in this question is the unequal weathering of different minerals.

Option A is correct because uneven dissolution and mineral alteration can produce a pitted or weakened layer. A change in Earth’s orbit does not directly create such a surface texture, and a river does not normally flow backward. The Moon cannot fall onto the rock in the stated way. The scientifically relevant process is differential weathering, in which mineral composition and resistance cause some parts of the rock to deteriorate faster than others.