For a gas to be soluble in water, the gas should contain molecules. The water should be at a temperature, and the gas should be at pressure above the surface of the water.

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.

level 4 to level 2 : ))