The question asks about the Earth's average temperature maintained by the natural greenhouse effect, without human influence. This refers to the planet's temperature before significant anthropogenic (human-caused) greenhouse gas emissions began to alter the climate.
Correct Option: B) 15°C
The natural greenhouse effect keeps the Earth's average temperature at a habitable 15°C. This is the baseline temperature that supports life on our planet.
The question asks to identify which of the given gases is NOT a greenhouse gas. To answer this, we need to understand what defines a greenhouse gas and then evaluate each option.
Correct Option: D) O2
Oxygen (\(\text{O}_2\)) is a diatomic molecule consisting of two identical oxygen atoms. Its symmetrical structure means that its vibrational modes do not result in a net change in its dipole moment. Consequently, it cannot absorb infrared radiation and therefore does not contribute to the greenhouse effect. It is not a greenhouse gas.
The question asks for the primary reason behind the increase in carbon dioxide (CO2) levels since the Industrial Revolution. This requires understanding the major anthropogenic and natural sources of CO2 and their relative impact over the specified historical period.
B) Human activities — Since the Industrial Revolution, human activities, primarily the burning of fossil fuels (coal, oil, and natural gas) for energy, industrial processes, and transportation, along with large-scale deforestation, have released enormous amounts of carbon dioxide into the atmosphere. This has significantly disrupted the natural carbon cycle and is the main reason for the observed rise in atmospheric CO2 levels.
The question asks about the primary role of tree root networks. We need to evaluate each option based on the known biological and ecological functions of tree roots.
C) Filter contaminants in soil — Tree roots, through their absorption capabilities and symbiotic relationships with soil microbes, can effectively take up and sometimes break down various pollutants and heavy metals, thereby acting as natural filters for soil and water.
The question asks about the primary aim of Project Surya. To answer this, one needs to recall the specific objectives and focus areas of this environmental initiative. Project Surya is a well-known project related to climate change and air pollution.
Correct Option: C) Reducing black carbon emissions
The question asks us to identify the correct statements regarding methane hydrates. We need to evaluate each statement individually based on scientific understanding of methane hydrates, their occurrence, and their environmental implications.
D) 1, 2 and 3 — All three statements are factually correct regarding methane hydrates, their distribution, and their atmospheric fate.