Is it true that carpets and curtains/drapes placed on the floor or wall surfaces can reduce noise level. Explain briefly?
Yes, it is true, that the placing/using carpets on floor and curtains on wall surface, windows, reduces noise level. This is because the curtains and carpets on wall surface and carpet acts as muffling device and absorb sounds of moderate level.
What is hybrid vehicle technology? Explain its advantages with a suitable example?
The technology used to run vehicles on dual mode like petrol or compressed natural gas is said to be hybrid vehicle technology. These vehicles runs on either petrol or CNG. As CNG is a clean and green fuel so it is helpful to reduce environmental pollution and also to conserve petrol, fossil fuel.
Is it true that if the dissolved oxygen level drops to zero, the water will become septic. Give an example which could lower the dissolved oxygen content of an aquatic body.
Yes, it is true, in case of zero level of dissolved oxygen (DO), the water becomes septic. Organic pollution like fertiliser in aquatic bodies is responsible for lowering (upto zero) the level of dissolved oxygen.
Name any one green house gas and its possible source of production on a large scale. What are the harmful effects of it?
The common green house gases are $\mathrm{CO}_2, \mathrm{CH}_4, \mathrm{CFC}$, oxide of nitrogen ( $\mathrm{N}_2 \mathrm{O}$ ), water vapour and $\mathrm{O}_3$. The level of $\mathrm{CO}_2$ (green house gas) is increasing due to large scale deforestation, change in land use and unlimited buring of fossils fuel and is leading to global warming.
The source of methane and other main green house gases are garbage dump, incomplete decomposition by anaerobic methanogens, flooded paddy field and marshy land. About 90-95\% of $\mathrm{CH}_4$ is produced/generated by rice fields of Asia.
It is a common practice to plant trees and shrubs near the boundary walls of buildings. What purpose do they serve?
A common practice to grow and maintain trees and shrub near the boundary wall of residential, official building acts as a barrier for sound and check noise pollution. This green belt of tree and shrub also acts as an effective measure to check primary air pollutants like dust, flyash, etc.