Class 8 Science Chapter 18 MCQ

Oxygen makes up about 21% of air by volume. It is essential for the survival of human beings.

Here, all the statements are correct. Hence, your answer will be option [D].

Windmill is not a source of air pollution. It is regarded as an alternative source of energy.

Here, all the statements are correct. Hence, your answer will be option [D].

Replace is not a way to conserve water. At our individual level, we should consciously save water and not to waste it. Reduce, reuse and recycle should be our “Mantra”.

The type of pollution which is likely to affect “Taj Mahal in Agra” to a greater extent is air pollution. It is affecting Taj Mahal by corroding it and yellowing its marble.

Carbon monoxide is produced by the incomplete combustion of fuel like wood, coal, kerosene, petrol and diesel.

The phenomenon of marble cancer is due to acid rain. Marble cancer is corrosion of buildings or monuments by acid rain.

Potable water is the water which is pure and fit for drinking. Water can be made potable by various methods such as boiling etc.

Here, all the statements are correct. Hence, your answer will be option [D].

Swimming in the pond is the activity which will produce least pollution of water.

“Van Mahotsav” is occasion when lakhs of trees are planted in July every year.

Here, all the statements are correct. Hence, your answer will be option [D].

Carbon dioxide, methane and water vapour a greenhouse gases. But the main constituents of the atmosphere nitrogen and oxygen are not greenhouse gases.

Here, all the statements are correct. Hence, your answer will be option [D].

All the living organisms in earth depend on only gas oxygen for respiration. Oxygen is produced only by plants and through photosynthesis. When fly ash and dust gets increased in air, the leaves are shed from sunlight. This reduces the rate of photosynthesis. The dust and fly ash also cause increase in leaf temperature, transpiration and stomatal conductance. This also leads to increase in carbon dioxide concentration and heat load.

Here, all the statements are correct. Hence, your answer will be option [D].

Tuberculosis is not caused by drinking of river water contaminated with untreated sewage. Tuberculosis is caused by the bacteria named Mycobacterium tuberculosis. It is an air-borne disease which is transferred when a person sneezes or coughs. Skin and blood test are taken to confirm tuberculosis in a person. The symptoms include cough with blood, weight loss, fever, chest pain, fatigue and loss of appetite. If it is left untreated, the affected person cannot be recovered and it will eventually lead to death.

As ozone absorbs high energy UVB and UVC energy waves from the sun and is broken down into atomic oxygen (O) and diatomic oxygen. Atomic oxygen is found prevalent in the upper stratosphere due to the bombardment of UV light and the destruction of both ozone and diatomic oxygen.

Drinking water can be made absolutely safe by adding some chlorine tablets. Chlorine is a traditional element which is used for purification of water. When chlorine is added to water, it reacts with water to produce hydrochloric acid. This acid kills the microbes present in water. But, the chlorine cannot kill all the harmful organisms present in the water. The over-usage of chlorine on water causes negative effect on the consumer. So, more advanced techniques are discovered for purifying water than adding chlorine tablets.

Fly ash is not a water pollutant. Generally, sewage, fertilizer and pesticide are used to defines the water with high concentration of impurities which are dirt and acid. Fly ash are particulates that are produced due to combustion of coal. This is mainly produced from factories that are powered using coals. Usually, the fly ash is purified from air with electrostatic precipitators. These particles are harmful because of presence of mercury, arsenic, lead and so on. Fly ash can increase the pH of water and soil and make it unfit for fish and plants. Respiration of fly ash by human causes severe respiratory problem.

Here, all the statements are correct. Hence, your answer will be option [D].

Dust is capable of preventing photosynthesis in plants. Dust have adverse effect in photosynthesis, leaf temperature, transpiration and stomatal conductance of plants. It has shading effect on plants. Photosynthesis is a phenomenon taking place in plants with carbon dioxide and water in presence of sunlight. Lack of any of the above-mentioned element reduces the rate of photosynthesis. The photons in sunlight is required for photosynthesis reaction. When the leaves are shaded, lack of sunlight occurs which reduces the rate of photosynthesis

Carbon monoxide does not lead to acid rain. Carbon dioxide, nitrogen dioxide and ‘Sulphur dioxide reacts’ with water to form the respective acid. Carbon monoxide does not react with water to form any acid. Now during rain these pollutants combine and react with the water droplets to form acid. This acid falls down on the ‘surface of the earth’ and forms acid rain. Acid rain when falls on skin or on plants chars the surface. In addition to this it destroys monuments and sculptures. Acid rain is immensely harmful in developing countries.

Earth is covered by a thin layer of ozone molecules (O₃). This layer protects the earth from the UV rays produced by sun. UV rays have harmful effect on all the living organisms in the earth. So, the UV-B rays and UV-C rays are absorbed by the ozone by a cyclic reaction. But, chlorofluorocarbons from the atmosphere disturb that cyclic reaction. Chlorofluorocarbons are one of the harmful gases produced by refrigeration system and aerosol sprays. This causes reduction in the ozone layers. So, the UV rays can reach the earth directly in large amount. Hence, your answer will be option [D].