The most harmful air pollutant produced by automobiles is- 

1. ${\mathrm{HNO}}_2$

2. NO

3. ${\mathrm{SO}}_2$

4. CO

Sewage water can be purified by

(1) Aquatic plant

(2) Microorganism

(3) Penicillin

(4) Fishes

Major pollutant in Jet plane emission is -

(1) $S{O}_2$

(2) CFC

(3) CO

(4) $CC{l}_4$

 B.O.D. is : 

(1) The amount of $O_2$ utilized by organisms in the water .

(2) The amount of $O_2$ utilized by microorganisms for decomposition .

(3) The total amount of $O_2$ present in water .

(4) All of the above . 

What is the intensity of sound in normal conversation 

1. 10 -20 decibal

2. 30 - 60 decibal

3. 70 - 90 decibal

4. 120 - 150 decibal

Which of the following is absent in polluted water

1. Hydrilla

2. Water hyacinth

3. Larva of stone fly

4. Blue green algae

Maximum green house gas released by which country

(1) India

(2) China

(3) U.S.A

(4) Britain

Ozone layer of upper atmosphere is being destroyed by

(1) Sulphur dioxide

(2) Carbon dioxide

(3) Chlorofluorocarbon

(4) Smog

The common nitrogen-fixer in paddy fields is
1. Azospirillum

2. Oscillatoria

3. Frankia

4. Rhizobium

The most hazardous metal pollutant of automobile exhaust is : 

1. Hg

2. Cd

3. Pb

4. Cu