Which of the following sets of rocks is organically formed?

The set of rocks that is organically formed is peat, chalk and limestone. Peat is formed by the accumulation of partially decayed organic matter in wetlands and is often used as fuel. Chalk is a soft, white, porous sedimentary rock composed of the shells of microscopic marine organisms. Limestone is a sedimentary rock composed mainly of calcium carbonate, which is also formed from the accumulation of the shells and skeletons of marine organisms. Therefore, peat, chalk, and limestone are all formed through the accumulation of organic matter or the remains of organisms, making them organic rocks. In contrast, the other options such as rock salt, breccia, conglometerate, clay, mudstone, sandstone, grit, coal, and shale are not formed through organic processes.