The answer is heat.
To use a glue gun, it has to use heat to heat up so that it can melt the glue.
A catalyst is a chemical that increases the rate of a chemical reaction without itself being changed by the reaction. The fact that they aren't changed by participating in a reaction distinguishes catalysts from substrates, which are the reactants on which catalysts work. Enzymes catalyze biochemical reactions.
The molecule that contains the fewest number of Hydrogen atoms would be B. Al(OH)3. It only has 3 Hydrogen atoms.
