Answer: Option B. -> Both A and R are true
:
B
The organic matter is decomposed by the microorganisms present in the soil or water. They do so with the help of enzymes that help them to digest complex organic molecules into simpler ones. But the micro-organisms present on the earth today lack such enzymes which will help them to digest plastic. Hence, plastic cannot be decomposed and becomesnon-biodegradable.

Answer: Option A. -> humans
:
A
Chemicals present in fertilisers and pesticides can enter inside soil or water bodies. From there, they can be taken up by aquatic or terrestrial plants and animals. Since, these chemicals are not degradable. They get accumulated at each trophic level. Human beings, are the top carnivores hence occupy the top level in the food chain. So, the maximum concentration of these chemicals will be accumulated in their bodies.

Answer: Option B. -> Product with carbon as major constituent
:
B
Compost is made out of organic substances which havecarbon as a major constituent. In other words, biodegradable substances are required for composting. Thus, the product should be made of biodegradable substances, usually organic.

Answer: Option A. -> True
:
A
An ecosystem is a community of living organisms in conjunction with the non-living components of their environment (things like air, water and minerals, light etc), interacting as a system. So, mountains are also a part of the natural ecosystem.

Answer: Option B. -> 2
:
B
Paper is biodegrdable and hence the bagsmade out of paper arealso biodegradable.Polyethene bags and waste parts of mobile phones or any other electronic devices (e-waste)are non-biodegradable.

Answer: Option B. -> they act as decomposers.
:
B
Microorganisms likebacteria and fungi, actasdecomposers as they break downcomplex organic substances into simpler inorganic substances that go into the soil. These inorganic substances are thenrecycled by plants.
Decomposers are considered to be of great importance as in theirabsence, earth would be filled with dead bodies.

Answer: Option C. -> 430 ppmv
:
C
430 ppmv is thecurrent concentration of $C{O}_2$in atmosphere.The global concentration of carbon dioxide in the atmosphere – the primary driver of recent climate change – has reached over 400 parts per million (ppm) for the first timethis year.The safe level of carbon dioxide in the atmosphere is 350 parts per million.

Answer: Option B. -> China
:
B
China is the country which has the largest number of hydroelectric dams. Hydropower doesn't pollute the air like power plants that burn fossil fuels, such as coal or natural gas. Hydropower is a domestic source of energy, produced in the United States. Hydropower relies on the water cycle, which is driven by the sun, thus it's a renewable power source.

Answer: Option A. -> O2
:
A
Ozone at the higher levels of the atmosphere is a product of UV radiation acting onoxygen $O_2$molecules.
$O_2$ $\stackrel{UV}{\to }$ $O$+$O$
$O$+$O_2$$\to$ $O_3$ (Ozone)
The sun propagates ultraviolet radiations which has an adverse effect on living beings. This layer absorbs the radiations and prohibits them from entering the outer surface of the earth.

Answer: Option A. -> True
:
A
The ecological niche describes how an organism or population responds to the distribution of resources and competitors and how it, in turn, alters those same factors. Anicheis the fit of a species living under specific environmental conditions.