Which of the following examples of rock is mostly likely to be weathered by the process of solution ?

Step 1: Analyze the question The question asks which rock is most likely to be weathered by solution, which is a chemical weathering process.

Step 2: The concept Solution (also called carbonation-solution) happens when rainwater absorbs carbon dioxide from the air and soil, forming a weak carbonic acid (H₂O + CO₂ → H₂CO₃). This acid reacts with rocks containing calcium carbonate (CaCO₃) and dissolves them.

The reaction is:

CaCO₃ + H₂CO₃ → Ca(HCO₃)₂ (calcium bicarbonate, which is soluble and gets washed away)

Step 3: Check each option

• A. Slates: a metamorphic rock formed from clay or shale. It is hard and fine-grained, and it does not dissolve easily.
• B. Graphite: pure carbon, chemically inert and very resistant to acids.
• C. Limestone: a sedimentary rock made mostly of calcium carbonate. It reacts readily with carbonic acid, so it dissolves easily.
• D. Granite: an igneous rock made of quartz, feldspar and mica. It is mostly weathered by hydrolysis or physical processes, not by solution.

Step 4: Answer Limestone is the rock most susceptible to solution. This is why limestone regions develop features such as caves, sinkholes, stalactites and stalagmites (karst scenery). In Nigeria, you can think of limestone areas like Nkalagu in Ebonyi State.

Exam tip: Remember "Limestone = Solution". Whenever you see carbonation or solution in a question, look for a carbonate rock such as limestone, chalk or dolomite.