Question

What must happen before a chemical reaction can begin?
The activation energy must be exceeded.
The activation energy must be reached.
The concentrations of products and reactants must be equal.
The concentration of reactant molecules must be reduced.

Answer 1

This is a very straight forward question.
We can rule out C and D because those are irrelevant.

Let's say you need 100 Joules to start an engine.

Would the engine start if you input 80J?
No.

Would the engine start if you input 120J?
Yes, but you only needed 100J

You don't need 120J, you don't need 100.99 J.
You need 100J

Answer 2

joules is just a unit of energy, don't focus too much on that. I hope this makes sense

Answer 3

To add to redbeardd, activation energy is the energy needed to "activate" the reaction. I hope that clears things up!