How do chemical weathering and the formation of biochemical sediment remove carbon from the atmosphere and store it in the geosphere?

The chemical weathering process of carbonation removes carbon from the atmosphere. In this process, carbon dioxide in the atmosphere mixes with rainfall to form carbonic acid. This acid then reacts with calcium carbonate or limestone to form calcium bicarbonate. This reaction removes carbon from the atmosphere. Organisms such as corals can remove dissolved carbon from oceans to form their hard rocky structures. Carbon dioxide from the atmosphere is dissolved in ocean water. Overtime they become limestone rock. 

C. which metal is less dense