Which of the following is the most stable ecosystem?
A. Mountain
B. Desert
C. Forest
D. Ocean

Hint: A stable ecosystem is the one which mete these three requirements: It is self-sustaining since the conditions for a stable ecosystem are present:
ENERGY is given by light to the ecosystem.
PLANTS are used to transform light energy into an organic energy molecule (glucose). RECYCLING of materials occurs during photosynthesis and respiration.

Complete answer:
In order for the environment to be deemed stable, processes need to be in place to help it return to its original state after a disruption has occurred. Areas with a high degree of biodiversity and genetic diversity are likely to have a more diverse ecosystem, with a range of food chains and biotic interactions.

Various natural and anthropogenic forces create and destroy mountains.
Similarly natural calamities may cause destruction of deserts and thus, they are not considered as a stable ecosystem.

> Forests can be destroyed by the process of deforestation or by natural factors such as fire hence, they cannot come under the category of stable ecosystem.

> Ocean is a stable ecosystem as it remains unchanged over the long term. Oceans have remained constant throughout the long history of the planet. Their scale is immense, so slight shifts in the oceans are not easy to notice.

Hence, The correct answer is option (D).

Additional information:
The integrity of the ecosystem is determined both structurally and functionally. The composition of the ecosystem comprises both biotic and abiotic elements. The working of the environment involves the transfer of energy and the cycling of minerals. The ocean is the most stable ecosystem. It is stable due to its natural liquid nature (saline), dissolved oxygen, light and temperature.

Note: An environment is considered to be stable when its structure and function remain unchanged for a long period of time. The ocean is the most stable ecosystem among the choices. The first explanation for its longevity is its chemical composition, which contains saline.