This rock is formed both chemically and organically.

This rock is formed both chemically and organically.

• A. Coal
• B. Limestone
• C. Shale
• D. Granite

Answer: (B)

Limestone forms both by chemical precipitation and by biological accumulation. Calcium carbonate can precipitate directly from seawater as the water chemistry changes, forming chemical sediment. At the same time, shells and skeletons of marine organisms like corals and mollusks accumulate as sediment and, when compacted and cemented, become limestone—an organic pathway. This dual formation is what makes limestone unique among the options. Coal is mainly from plant material (organic), granite forms from cooled magma (igneous), and shale comes from fine mud and clay deposited in water (not primarily chemical precipitation or biogenic buildup).

Limestone forms both by chemical precipitation and by biological accumulation. Calcium carbonate can precipitate directly from seawater as the water chemistry changes, forming chemical sediment. At the same time, shells and skeletons of marine organisms like corals and mollusks accumulate as sediment and, when compacted and cemented, become limestone—an organic pathway. This dual formation is what makes limestone unique among the options. Coal is mainly from plant material (organic), granite forms from cooled magma (igneous), and shale comes from fine mud and clay deposited in water (not primarily chemical precipitation or biogenic buildup).