Answer:
make them mark me brainliest after answering them
Explanation:
1. Electrons travel around the nucleus in fixed energy levels with energies that vary from level to level
2.protons, neutrons, and electrons have a mass, but electrons have far less mass
3.cations and protons
4. idk
Answer:
Coefficient required to balance chemical reaction are simply called stoichiometry
Answer:
Scientists believe that the different types we know emerged as early humans adapted to infectious diseases.
Explanation:
Different human blood types probably emerged to ward off infectious diseases. The incompatibility of some blood types, however, is only an "accident" of evolution. But this is a relatively recent problem, since blood transfusion has been around for only a few hundred years.
There are four main blood types. The oldest is B, which must have originated about 3.5 million years ago - it existed even before the human species evolved from its hominid ancestors, from a genetic mutation that modified one of the sugars in the surface of red blood cells.
Approximately 2.5 million years ago, mutations inactivated sugar, resulting in type O blood, which has neither type A nor B. sugar. AB blood, as it is easy to suppose, is covered by both sugar A and sugar by B.
The role of a pioneer species is to produce the soil.
