The answer is D) a neutron.
When we say an atom's mass is, like 5 atomic mass units actually we are saying that the total number of the neutrons and protons in its nucleus is 5.
The mass of a neutron and a proton is each one atomic mass unit.
Mass of a neutron is approximately 1 atomic mass unit.
Do you have a picture of where you go this question from?
Answer:
The sum of each elementary step in a reaction mechanism must yield the overall reaction equation. From the rate law of the rate-determining step it must agree with the experimentally determined rate law. The rate-determining step is the slowest step in a reaction mechanism. Because it is the slowest, it determines the rate of the overall reaction.
Explanation: