Question

1. a catalyst is essential to start a reaction, and also to ______.

keep the reaction going
change the reaction
stop the reaction
cancel the reaction

Explanation:

A catalyst speeds up a chemical reaction by providing an alternative reaction pathway with lower activation energy. It does not start a reaction (reactions can start without a catalyst, just slower), but it helps the reaction proceed faster, which can be thought of as keeping the reaction going more efficiently. It does not change the nature of the reaction (the reactants and products remain the same), stop the reaction, or cancel the reaction.

Answer:

keep the reaction going