Solution weathering is most effective in which material?

Correct answer: Soluble minerals such as rock salt and gypsum

Direct answer: Option A, soluble minerals such as rock salt and gypsum. Solution weathering occurs when water dissolves minerals directly. The rate is especially high where the material is readily soluble and water can reach it repeatedly. Rock salt is a very clear example, and gypsum is also relatively soluble compared with resistant minerals. Option A is therefore correct. Option B is wrong because quartz is hard and generally resistant to direct dissolution under ordinary surface conditions. Option C is not the best answer because dry ash has little available water, and the wording does not identify a readily soluble mineral undergoing solution. Option D is wrong because a completely waterproof metal does not allow water to dissolve it in the way described. Solution is different from physical breaking: the material enters the water as dissolved chemical matter. Memory cue: if the question says solution weathering, look first for salt, gypsum, limestone and water; among these options, salt and gypsum give the clearest answer.