Which condition helps salt weathering?

Correct answer: Entry and drying of salty water

The direct answer is A, entry and drying of salty water. Salt weathering occurs when salty water enters cracks or pores in rock and later evaporates. Step by step: salty water moves into a small opening; warm or dry conditions remove the water by evaporation; salt crystals are left behind and may grow; the growing crystals press against the walls of the opening; repeated wetting and drying can loosen grains and break the rock. Option A is correct because the wet-dry cycle supplies both salt and crystal growth. Option B is wrong because complete darkness without water provides no dissolved salt or wet-dry process. Option C is wrong because volcanic eruptions are not the normal cause of salt crystallisation in exposed rocks. Option D is wrong because plate collision may create mountains and pressure, but it is not the direct condition needed for salt weathering. Remember: salt weathering needs salt, water, evaporation, and repeated cycles.