71.

Eutrophication of a lake means, it

• is low is nutrients

• is high in nutrients

• has a high temperature

• has excess amount of organic matter

Which one of the following is mainly responsible for depletion of ozone layer?

• Methane

• Carbon dioxide

• Water

• Chlorofluorocarbons

Photochemical smog is due to the presence of:

• Oxides of sulphur.

• Oxides of nitrogen.

• Oxides of carbon.

• Chlorofluoro carbons.

Which of the following is secondary pollutant?

• CO₂

• N₂O

• PAN

• SO₂

In which part of the atmosphere, does the freon remain unchanged?

• Stratosphere

• Troposphere

• Mesosphere

• Thermosphere

Which one of the following elements, is a component of a compound essential for photosynthesis ?

• Iron

• Calcium

• Barium

• Magnesium

Photochemical oxidants, i.e. PAN or PBN are formed by:

• action of nitrogen oxides on hydrocarbons in presence of sunlight

• action of CO₂ on hydrocarbons in presence of sunlight

• action of hydrogen sulphide on hydrocarbon in presence of sunlight

• None of the above

Use of chlorofluorocarbons is not encouraged because :

• they are harmful to the eyes of peoplethat use it

• they damage the refrigerators and air conditioners

• they eat away the ozone in the atmosphere

• they destroy the oxygen layer

Alum is a water purifier, because it :

• coagulates the impurities

• softens hard water

• gives taste

• destroys the pathogenic bacteria

Ozone layer is being depleted. This is due to :

• NO (nitric oxide) emission from supersonic jets

• chlorofluoro carbon used as aerosols

• Both (a) and (b)

• None of the above