The chemical reactions shown in this sequence are:

C (carbon) reacts with 2H2 (hydrogen) to form CH4 (methane).CH4 (methane) reacts with 2O2 (oxygen) to form CO2 (carbon dioxide).CO2 (carbon dioxide) reacts with 2NaOH (sodium hydroxide) to form Na2CO3 (sodium carbonate).Na2CO3 (sodium carbonate) reacts with CaCl2 (calcium chloride) to form CaCO3 (calcium carbonate).

This sequence demonstrates the transformations that carbon undergoes in these chemical reactions, leading to the formation of calcium carbonate.