B.O.D is-

1.	The amount of O2 utilized by organisms in the water.
2.	The amount of O2 utilized by microorganisms for decomposition.
3.	The total amount of O2  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

The ozone layer of the upper atmosphere is being destroyed by : 

1. Sulphur dioxide

2. Carbon dioxide

3. Chlorofluorocarbon

4. Smog

Most hazardous metal pollutant of automobile exhaust is

(1) Hg

(2) Cd

(3) Pb

(4) Cu

$S{O}_2$ pollution is indicated by

1. Grasses

2. Mosses

3. Lichens

4. Fossils

B.O.D is connected with

(1) Organic matter

(2) Microbes

(3) Both

(4) None

Acid rain is due to an increase in the atmospheric concentration of : 

1. Ozone, and dust

2. $C{O}_{\mathrm{2,}}$ and CO

3. $S{O}_{\mathrm{3,}}$ and CO

4 $S{O}_{\mathrm{2,}}$ and $N{O}_2$

Soil erosion is greater when

(1) No rain occurs

(2) Winds do not blow

(3) The rainfall is evenly distributed

(4) The Rainfall is received in heavy down pour