In general, as activation energy increases, reaction rate
a) goes down regardless of whether the reaction is exothermic or endothermic
b) goes down if the reaction is exothermic
c) goes down if the reaction is endothermic
d) stays the same regardless of whether the reaction is exothermic or endothermic
e) none of the above

a)goes down regardless of whether the reaction is exothermic or endothermic

Explanation:

The activation energy is the minimum amount of energy required for a chemical reaction to commence. As this increases, the reaction will become slower because it must overcome this barrier.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.