An element is a pure substance
Oxygen is a pure substance, as it is composed of only a single kind of atom. Which is the oxygen atom, it cannot be broken or degraded down any further into constituents that make up the element. In terms of both chemically and physically.
Vaporization and Production of bubbles. Production of heat and melting are physical changes
Ecological succession is the steady and gradual change in a species of a given area with respect to the changing environment. it is a predictable change and is an inevitable process of nature al all the biotic components have to keep up with the changes in our environment.
