What word means the gradual change and build up of organisms in an enviroment

Does the number of ions in solution increase, decrease, or remain constant? it continuously decreases. it continuously increases. it decreases at first, then increases. it increases at first, then decreases.

If a computer chip switches off -on-off in 0.015 us, what is the switching time in nanoseconds?

Just on number 2 (all parts), and if you do answer explain in detail