Final answer:
The least likely major component of marine sediments is organic matter, with sand, clay, and limestone being more prominent due to their inorganic nature and processes of deposition and compaction. Option number 3 is correct.
Step-by-step explanation:
The least likely major component of marine sediments among the options given is organic matter. Marine sediments are typically composed of various materials, such as sand, clay, limestone, and other elements derived from rock weathering, chemical precipitation, and biological processes. Sand is often found close to shorelines and is primarily composed of quartz grains.
Clay forms from the weathering of feldspar and gets deposited further away from the source rock. Limestone, which includes various forms such as chalk and fossiliferous limestone, is usually formed from accumulated biological material like shells and coral that get compacted over time into rock. However, organic matter, while present in marine sediments, is less likely to be a major component compared to inorganic materials like sand, clay, and limestone because it needs to be buried quickly to avoid decay and it does not form a dominant part of the sediment's bulk composition.