The second one would be one of the application of an endothermic reaction as because endothermic reaction always have the heat in the process to mix the reactants and form the products as here in a burning wood when the wood is supplied with heat then it change into products as ashes and smoke fumes So here due to the heat is involved to form the products thats the reaction is endothermic reaction.
Because the density are v/mass not mass only so the one that floats have a density less than 1 and the one that sinks have a density more than 1 {(1) is the water density}
