Free Environmental Chemistry MCQs with Answers

111. The increasing number of CFC production for industrial use has been a major contributor to the depletion of ozone molecules in the stratosphere. When CFCs diffuses slowly to the atmosphere in the presence of UV light between 175 nm to 220 nm, the ozone layer decomposes. If 1 mole of CFCl3 (Freon - 110) has been released into the air, how many moles of oxygen is produced from the photodecomposition of ozone?

• A. 1
• B. 2
• C. 3
• D. 4

Explanation: The photodecomposition of one molecule of CFCI3 can destroy one ozone molecule, as shown in the following equation:CFCI3 + UV light → CFCl2 + Cl•Cl• + O3 → ClO• + O2ClO• + O → Cl• + O2Therefore, for every mole of CFCI3 photodecomposed, one mole of ozone is destroyed. Therefore, if 1 mole of CFCI3 is released, 1 mole of ozone will be destroyed. Since each ozone molecule is composed of 2 oxygen atoms, 2 moles of oxygen will be produced from the photodecomposition of 1 mole of ozone. Therefore, the answer is B) 2.

112. In the atmosphere, CO2 is about?

• A. 0.01 %
• B. 0.03 %
• C. 0.05 %
• D. 0.09 %

Explanation: The proportion of carbon dioxide in the atmosphere is about 0.03%Carbon dioxide is an important long-lived trace gas in Earth's atmosphere currently constituting about 0.03% of the atmosphere.Carbon dioxide concentrations are rising mostly because of the fossil fuels that people are burning for energy.Fossil fuels like coal and oil contain carbon that plants pulled out of the atmosphere through photosynthesis over the span of many millions of years

113. The unit _ is commonly used by meteorologists.

• A. Bar
• B. Centibar
• C. Millibar
• D. Kilobar

Explanation: Millibar is a metric unit of pressure commonly used by meteorologists.

114. Which of these pollutants is produced by burning of coal and causes acid rain:

• A. NO
• B. CO2
• C. SO2
• D. CO

Explanation: SO2 is emitted by the burning of fossil fuels - coal, oil, and diesel. SO2 and other sulfur oxides can contribute to acid rain which can harm sensitive ecosystems.Nitrogen oxides are produced in combustion processes, partly from nitrogen compounds in the fuel, but mostly by direct combination of atmospheric oxygen and nitrogen in flames. They also contribute to acid rain.CO2 is a product of combustion reaction and is a greenhouse gas.Carbon monoxide (CO)-a colorless, odorless, tasteless, and toxic air pollutant-is produced in the incomplete combustion of carbon-containing fuels, such as gasoline, natural gas, oil, coal, and wood. It can cause carbon monoxide poisoning.

115. Which of the following gas, when ignited, burns with a blue flame and is not very soluble in water?

• A. O2
• B. CO2
• C. N2
• D. He

Explanation: Firstly we should be clear that each gas has a specific type of flame depending on the nature of combustion and the products formed and so does all these gases which are given in the option. Nitrogen when ignited in the presence of oxygen it forms various oxides of nitrogen like NO, NO2 and burns with a blue flame.

116. Percentage of nitrogen by volume in air is:

• A. 78%
• B. 50%
• C. 20%
• D. 98%

Explanation: By volume, the dry air in Earth's atmosphere is about 78.08 percent nitrogen, 20.95 percent oxygen, and 0.93 percent argon. A brew of trace gases accounts for the other approximately 0.04 percent, including the greenhouse gases carbon dioxide, methane, nitrous oxide and ozone.

117. Which of the following would react with ozone in the atmosphere?

• A. F*
• B. O2
• C. O*
• D. Cl*

Explanation: Chlorine and bromine atoms are also known as free radicals. Other free radicals in the stratosphere can also remove ozone. The chlorine atoms react with ozone to produce chlorine oxide and O2 molecules. The chlorine oxide molecule is also very reactive and can react with oxygen atoms to regenerate the chlorine atom, hence catalysing the destruction of the ozone layer.

118. [Ti(H2O)6]3+ transmits:

• A. Yellow and Red light
• B. Yellow and Blue light
• C. Red and white light
• D. Red and blue light

Explanation: When white light is allowed to fall on [Ti(H2O)6]3+ ion, this ion absorbs the light of green and yellow colour and transmits almost purple colour. Red and Blue are transmitted.

119. About 80% of ammonia is used for the production of:

• A. Explosives
• B. Fertilizers
• C. Nylon
• D. Polymers

Explanation: About 80% of the ammonia produced by industry is used in agriculture as fertilizer. Ammonia is also used as a refrigerant gas, for the purification of water supplies, in the manufacture of plastics, explosives, textiles, pesticides, dyes and other chemicals.About 80% of ammonia is used for the production of fertilizers.Ammonia (NH3) is a key component in the production of nitrogen-based fertilizers. Ammonia can ber eacted with various substances, such as nitric acid or sulfuric acid, to produce ammonium nitrate or ammonium sulfate, which are commonly used fertilizers. These fertilizers provide essential nitrogen top lants, promoting their growth and enhancing crop yields.

120. Urea is the most widely used nitrogen fertilizer in Pakistan. Its composition is:

• A. NH2CO
• B. N2H5CO2
• C. N2H4CO2
• D. N2H4CO

Explanation: Urea, also known as carbamide, is an organic compound with the chemical formula CO(NH2)2. This amide has two -NH2 groups joined by a carbonyl (C=O) functional group.The composition of urea, which is the most widely used nitrogen fertilizer in Pakistan, is N2H4CO.Urea has the chemical formula CO(NH2)2, which can also be represented as NH2CONH2. This indicates that urea consists of two amine groups (NH2) attached to a carbonyl group (C=O). The structure of urea is shown as N2H4CO, representing the arrangement of atoms.