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

174.

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

Which of the following has highest concentration of PAN?

• Smoke

• Ozone

• Photochemical smog

• Reducing smog

Which of the following is not a greenhouse gas?

• Carbon dioxide

• Water vapours

• Methane

• Oxygen

Living in the atmosphere of CO is dangerous, because it

• combines with O, present inside to form CO₂

• reduces organic matter of tissues

• combines with haemoglobin and makes it incapable to absorb oxygen

• dries up the blood.

Which of the following is not a green house gas?

• Hydrogen

• Carbon dioxide

• Methane

• Nitrous oxide or N₂O