Which is most stable ecosystem?

In an ecosystem:

The most stable ion is

Artificial sweetener which is not stable at cooking temperature is :

Ecosystem is

Which of the following is an abiotic component of the ecosystem?

A man made ecosystem is

Which of the following ecosystems is most productive in terms of net primary production?

Unlike "In"^+, Tl^+ is most stable with respect to disproportionation reaction.

A diagrammatic representation of different trophic levels in an ecosystem is given below What is the difference between a food chain and food web? Which one is more stable?