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<u>Answer:</u> The correct option is
<u>Explanation:</u>
A catalyst is defined as the chemical species that increases the reaction rate but does not participate in it and is left behind after the completion.
A homogeneous catalyst is one that is present in the same phase as the reactants and products.
A heterogeneous catalyst is one that is present in different phase as that of reactants and products.
For the given chemical reaction:

As all the reactants and products are in gaseous state so, the homogeneous catalyst must also be in the gaseous state only.
Hence, the correct option is 
It requires more energy to boil an substance than to melt it (with special exceptions). When something is boiled you are furthering the distance between the already stretched out molecules which will require more energy to do so, also in most cases you will be creating a vapor from boiling which has a high kinetic energy value.