Q.1. What is doubling time?
Ans. Doubling time is the number of years required for the population of an area to double its present size. Population doubling time is useful to demonstrate the long-term effect of a growth rate, but should not be used to project population size.
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Q.2. Define replacement level.
Ans. Replacement level is the level of fertility at which a couple has only enough children to replace themselves, or about two children per couple but due to infant mortality rate this replacement level is usually changed. In developed countries with low child mortality, replacement level is below approximately 2.1 children per woman’s life time.
Q.3. What is total fertility rate?
Ans. Total Fertility Rate (TFR) is the average number of children each woman would have in her life time, assuming that current age-specific birth rates remain constant throughout her child bearing years.
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Q.4. What is meant by population pyramid?
Ans. Age structure of population of a nation can be represented by population pyramid (age pyramids) based upon people belonging to different age classes. The reproductive status of the population depends on proportion of individuals of pre-reproductive (0-14 years), reproductive (15-44 years) and post reproductive (45 years and above) stages.
Q.5. Name the gases and reactions causing acid rain.
Ans. Acid rain is caused by oxides of sulpher and oxides of nitrogen, when these pollutants reach into the atmosphere, react with rain water and form acid. The main reactions are as follows: 2S02
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2SO2 + O2 = 2SO3
2NO + O2 = 2NO2
SO3 + H2O = H2SO4
NO2 + H2O = HNO2 + HNO3
Q.6. How ozone layer does protect us?
Ans. Ultraviolet (UV) radiations emitted from the Sun are harmful to the skin and is the main cause of sunburn; excessive exposure can also cause genetic damage, resulting in problems such as skin cancer. The ozone layer absorbs most of the harmful UV wavelengths (270315 nm) and protects us.
Q.7. Write Short notes on:
(i) Ozone layer depletion
(ii) Acid rain
Ans. (i) The term Ozone depletion is a slow, steady decline, of about 3% per decade, in the total amount of ozone in the earth’s stratosphere during the past twenty years and seasonal decrease in stratospheric ozone over the earth’s polar regions during the same period.
(ii) Acid rain is caused by oxides of sulpher and oxides of nitrogen, when these pollutants reach into the atmosphere, react with rain water and form acid. The main reactions are as follows.
2SO2 + O2 = 2SO3
2NO + O2 = 2NO2
SO3 + H2O = H2SO4
NO2 + H2O = HNO2 + HNO3
Q.8. Mention the causes Acid rain
Ans. Two elements, sulphur and nitrogen, are primarily responsible for the harmful effects of acid rain. The sulphur combines with oxygen to form sulphur dioxide. Because sulphur dioxide does not react with most chemicals found in the atmosphere, it can travel long distances. Eventually, if it comes in contact with ozone or hydrogen peroxide, it can be converted to sulphur trioxide.
Sulphur trioxide can dissolve in water, forming a dilute solution of sulfuric acid. NOx is the sum of nitrogen oxide and nitrogen dioxide in a given parcel of air. These can dissolve in water, forming weak solutions of nitric and nitrous acids.
Q.9. Name the gases and reactions causing acid rain.
Ans. Acid rain is caused by oxides of sulpher and oxides of nitrogen, when these pollutants reach into the atmosphere, react with rain water and form acid. The main reactions are as follows:
2SO2 + O2 = 2S03
2NO + O2 = 2NO2
SO3 + H2O = H2SO4
NO2 + H2O = HNO2 + HNO3
Q.10. How ozone layer does protect us?
Ans. Ultraviolet (UV) radiations emitted from the Sun are harmful to the skin and is the main cause of sunburn; excessive exposure can also cause genetic damage, resulting in problems such as skin cancer. The ozone layer absorbs most of the harmful UV wavelengths (270315 nm) and protects us.
Q. 11. Write Short notes on:
(i) Ozone layer depletion
(ii) Acid rain
Ans. (i) The term Ozone depletion is a slow, steady decline, of about 3% per decade, in the total amount of ozone in the earth’s stratosphere during the past twenty years and seasonal decrease in stratospheric ozone over the earth’s polar regions during the same period.
(ii) Acid rain is caused by oxides of sulpher and oxides of nitrogen, when these pollutants reach into the atmosphere, react with rain water and form acid. The main reactions are as follows.
2SO2 + O2 = 2SO3
2NO + O2 = 2NO2
SO3 + H2O = H2SO4
NO2 + H2O = HNO2 + HNO3