Limestone
Explanation:
Sedimentary rocks are formed by the accumulation of sediments. In this question box X is a nonclastic rock that can be chemical sedimentary rock or organic sedimentary rock. In given options, Breccia, Sandstone, and Conglomerate are clastic sedimentary rocks. Only Limestone is non-clastic rock, that belongs to organic sedimentary rocks. Limestone form from the accumulation of plant or animal debris.