When a single compound breaks down into two or more compounds or elements in a chemical reaction then it is known as decomposition reaction.
The chemical symbol for sodium carbonate is
.
The decomposition of sodium carbonate is:

The decomposition of sodium bicarbonate,
will result in the formation of sodium oxide,
and carbon dioxide,
.
Hence, carbon dioxide,
will produce with sodium oxide,
on decomposition of
.
Answer:
magnesium + oxygen ----> magnesium oxide
The correct option is B. To get the number of atom for each compound, each element in the compound will be counted as an atom. For instance, for Fe[ClO4]2, there are 1 atom of Fe, 2 atoms of Cl, and 8 atoms of O, making a total of 11 atoms [1 + 2 + 8= 11]. The other options have less than 11 atoms.