What do oxygen, silicon, and selenium have in common? How might this relate to their organization on the periodic table?

They all belong to the p block in the periodic table

Explanation:

Let us examine the electronic configuration of each element;

Oxygen - [He] 2s2 2p4

Silicon - [Ne] 3s2 3p2

Selenium - [Ar] 4s2 3d10 4p4

A common thread that joins all the elements listed above is that they all belong to the p-block in the periodic table. They could be collectively referred to as p-block elements.

"the periodic table is arranged in order of atomic number."

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.