Answer:
Mark me brainlist I will then answer in comment
I’m almost sure it’s D but i could be wrong
On Earth it is relatively rare—5.2 ppm by volume in the atmosphere. Most terrestrial helium<span> present today is created by the natural radioactive decay of heavy radioactive elements (thorium and uranium, although there are other examples), as the alpha particles emitted by such decays consist of </span>helium<span>-4 nuclei.</span>
Yes, people should be concerned because plaque buildup might cause your breath to smell bad, or cause your teeth to look very yellow, consider brushing your teeth and using mouth wash daily and don’t drink or eat unhealthy foods that will cause your teeth to look bad. plaque buildup might also cause damage to the stomach and maybe affect when you have to use the restroom.
Chemical change. Made my answer simple enough and I hope it becomes brainiest. Happy to help!