Explanation:

The word ‘sedimentary’ is derived from the Latin word sedimentum, which means settling. Rocks (igneous, sedimentary and metamorphic) of the earth’s surface are exposed to denudational agents, and are broken up into various sizes of fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits through compaction turn into rocks. This process is called lithification. In many sedimentary rocks, the layers of deposits retain their characteristics even
after lithification. Hence, we see a number of layers of varying thickness in sedimentary rocks like sandstone, shale etc.
• Depending upon the mode of formation, sedimentary rocks are classified into three major groups:
o Mechanically formed — sandstone, conglomerate, limestone, shale, loess etc.
o Organically formed — geyserite, chalk, limestone, coal etc.
o Chemically formed — chert, limestone, halite, potash etc..
• Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale type
sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the
finest grained foliated metamorphic rock.
• Hence option b is the correct answer