Question

when two intermediate chemical equations are combined, the same substance that appears in the same phase can be canceled out provided that

it is a reactant in both of the intermediate reactions.
it is a product in one intermediate reaction and a catalyst in the other reaction.
it is a reactant in one intermediate reaction and a product in the other reaction.
it is a reactant in one intermediate reaction and a catalyst in the other reaction.

Explanation:

In chemical reactions, when combining intermediate equations, a substance can be canceled out if it is a reactant in one intermediate - reaction and a product in the other. This is because it is consumed in one step and produced in another, effectively not being part of the overall reaction. A substance cannot be canceled if it is a reactant in both reactions or has a role as a catalyst in one of the reactions in the way described in the other options.

Answer:

It is a reactant in one intermediate reaction and a product in the other.