Rust is a compound of iron and oxygen. Compare the properties of rust, iron, and
oxygen by filling in the missing cells in
the table above. What can you conclude
about the properties of compounds and
their elements?

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.

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.