The bohr model of the atom addressed the problem of
a.) why electrons didn't fall into the positive nucleus
b.) how so many positive charges could be crowded into such a small space in the nucleus
c.) how so much energy could be released from an atom
d.) all of the above

A.) why electrons didn't fall into the positive nucleus

Explanation:

In the year 1913, Danish atomic physics expert Niels Bohr (1885-1962) established the atomic model planetary system that is currently used. With this model Bohr explained why the electron does not fall into the nucleus. According to him this occurs the electrom can not since its orbits are like steps of a ladder.

For better understanding, we can imagine the atom as a kind of tiny football field.  The nucleus is in the center of the lawn and electrons can run around the grandstand steps. From time to time, the electrons jump from one step to another, if they go up they use energy, down they release energy. However, electrons can never leave the stands and invade the field. Bohr did not explain why the ban, but the model worked well enough to make it clear that it had elements of the final explanation.

one negative thing it that it can kill water animals. another negative thing is it can cause the destruction of ecosystem. one way water pollution can be reduced is to conserve energy.