Question

If water pollution continues at its present rate, it will eventually:
A. Stop water cycle
B. Prevent precipitation
C. Make oxygen molecules unavailable to water plants
D. Make nitrate molecules unavailable to water plants

Answer 1

Water is highly essential for all living organisms. Almost every kind of reaction taking place on this planet earth is highly dependent on the presence of water in one form or the other. However, water pollution caused by release of toxic materials in water is producing many hazards like lowering the concentration of dissolved oxygen.

Complete step by step answer:
Dissolved oxygen in water is of utmost importance for aquatic life. If the dissolved oxygen concentration is less than 6 ppm, then the fish growth is inhibited. Lower the concentration of dissolved oxygen in water, the more polluted is the water sample.
The sources of dissolved oxygen in water are the dissolution of oxygen at the surface of water from the atmosphere and the process of photosynthesis in water having green aquatic plants.
In this case, water is supersaturated with oxygen during daylight. But after dark, photosynthesis stops but the plants still continue to respire. This leads to the reduction in the amount of dissolved oxygen in water.
The deoxygenation of water can take place by certain processes. The dissolved oxygen in water may be consumed by the bio-oxidation of nitrogen containing materials.
${\text{N}}{{\text{H}}_{\text{4}}}^{\text{ + }}\left( {{\text{aq}}} \right){\text{ + 2}}{{\text{O}}_{\text{2}}}\left( {{\text{aq}}} \right) \to 2{{\text{H}}^{\text{ + }}}\left( {{\text{aq}}} \right){\text{ + N}}{{\text{O}}_{\text{3}}}^{\text{ - }}\left( {{\text{aq}}} \right){\text{ + }}{{\text{H}}_{\text{2}}}{\text{O}}\left( {\text{l}} \right)$
The dissolved oxygen in water may also be consumed by the oxidation of organic matter by microorganisms.
$\left[ {{\text{C}}{{\text{H}}_{\text{2}}}{\text{O}}} \right]\left( {{\text{aq}}} \right){\text{ + }}{{\text{O}}_{\text{2}}}\left( {{\text{aq}}} \right) \to {\text{C}}{{\text{O}}_{\text{2}}}\left( {{\text{aq}}} \right) + {{\text{H}}_{\text{2}}}{\text{O}}\left( {\text{l}} \right)$
It can also be consumed by the chemical oxidation of chemical reducing agents. For example,
${\text{4F}}{{\text{e}}^{{\text{2 + }}}}\left( {{\text{aq}}} \right) + {{\text{O}}_{\text{2}}}\left( {{\text{aq}}} \right) + 10{{\text{H}}_{\text{2}}}{\text{O}}\left( {\text{l}} \right) \to {\text{4Fe}}{\left( {{\text{OH}}} \right)_3}\left( {\text{s}} \right){\text{ + 8}}{{\text{H}}^{\text{ + }}}\left( {{\text{aq}}} \right)$

Hence, the correct option is C.

Note: Water pollution also creates hazards for aquatic animals. Organic chemicals like pesticides, fertilizers, synthetic detergents, food additives, plasticizers are mostly toxic in nature and contribute towards water pollution. The addition of phosphates in the form of fertilizers and detergents leads to the formation of algae which decreases the dissolved oxygen concentration. This is known as eutrophication and inhibits the development of fish. Sediments like silt, sand etc. also cover the fish nests, eggs laid by them and their food supplies. They also reduce the amount of light supply to aquatic animals.