In this question, we are asked to spot the odd item from the given options. The options listed are shale, marble, limestone, and sandstone. Shale, limestone, and sandstone are all types of sedimentary rocks, which means they are formed from the accumulation and compression of loose materials over time. However, marble is not a sedimentary rock but a metamorphic rock. It is formed from the transformation of limestone or dolomite through intense heat and pressure. Therefore, the odd item in this list is option 2, marble.

Note: The provided answer is correct.