Describe the amount of time needed for complete ecosystem recovery

A recovery is hugely dependent on a number of factors, and the time needed may vary from months to hundreds of years.

The parameters that need to be considered:

type of ecosystem - terrestrial or aquatic; if aquatic - stagnant or flowing body of water; fresh water, salt water, or brackish; tidal or stable; etc.
productivity - may be high, low, or somewhere in between; length of the growth season, which may vary from several weeks to year-round;
climate - tropical, subtropical, temperate, subpolar, polar;
amount of precipitation;
seasonality - one, two, or four seasons; duration of seasons;
kind of damage - disturbance, devastation (fire or volcanic ash); toxic materials; overpopulation and population explosion; elimination of species; extent of damage (area and severity).
migratory potential of species that are capable of re-populating the area.
resilience of the ecosystem - how much soil, how resistant it is to erosion.
A fast flowing stream may recover quickly from a single disruptive event, such as influx of noxious materials, especially if it can be populated from up-stream areas. On the opposite end there are old-growth forests, that may take hundreds of years to re-form the interactions between plants, fungi, and lichens, if a patch of a forest was completely devastated or subjected to clear cutting. On the other hand, the effect of a brush fire in a forest may be hardly noticeable after one growing season. A tropical forest typically has a thin layer of soil and can undergo denudation after clearcutting - and a complete recovery may take very long time, if it is possible at all. Tundra may recover slowly, because of a very short growth season; alpine ecosystems are typically fragile, easy to damage, and slow to recover.

Answer:

a. energy is absorbed in the reaction.

explanation:

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.