which of the following is true regarding activation energy?
a. lt does not hold up a reaction from starting
b. it is required only in endothermic reactions
c. this energy usually comes in the form of light or heat
d. it is required only in exothermic reactions

Option (C) is the correct answer.

Explanation:

Activation energy is defined as the minimum amount of energy required by the molecules of a reactant to undergo a certain reaction.

Therefore, when energy in the form of heat or light is provided to a substance then its molecules gain kinetic energy. As a result, molecules have gained activation energy to carry out a reaction.

Thus, we can conclude that statement true regarding activation energy is that this energy usually comes in the form of light or heat.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.