Which gas sample contains the most molecules ?

CO2

Explanation:

(a) CO2; according to Avogadro's Hypothesis, they all contain the same number of particles, therefore, the heaviest molecule, CO2 (molar mass = 44), will have the greatest mass. (b) all the same; at the same temperature all gases have the same kinetic energy.

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.