Answer: Option A. -> carbon dioxide
:
A
Global warming is caused by green house gases like carbon dioxide, water vapour, methane etc. Global warming is the steady rise of the Earth's average temperature.

Answer: Option B. -> Smog
:
B

During winters, a thick fog-like layer is seen in the atmosphere especially in developing cities. This is called smog which is made up of smoke and fog. Smoke may contain oxides of sulphur and nitrogen which combine with other air pollutants and fog to form smog. Smog causes breathing difficulties such as asthma, cough and wheezing.

Answer: Option A. -> Sulphur dioxide
:
A and C

Acid rain results when sulphur dioxide,$S{O}_2$ and nitrogen oxides ($NO$ and $N{O}_2$) are released into the atmosphere and are transported by the wind and air currents. These oxides  react with water, oxygen and other chemicals to form sulphuric acid and nitric acid. These acids fall to the ground as Acid Rain. While a small portion of the gases that cause acid rain is from natural sources such as volcanoes, most of it comes from the burning of fossil fuels.

Answer: Option A. -> $\text{CO}$
:
A
Carbon monoxide is a colourless, odorless, tasteless, non-irritating and toxic gas formed by incomplete combustion of organic matter. It mainly causes adverse effects by combining with haemoglobin to form 'carboxyhaemoglobin' in the blood. This prevents haemoglobin from carrying oxygen to the tissues, leading to asphyxiation (choking and shortness of breath). In extreme conditions, it can also cause death.

Answer: Option B. -> air pollution
:
B

Air pollution is the phenomenon in which air is contaminated by unwanted substances. These contaminants have harmful effects on both living and non-living things.

Examples: Air pollution is caused by CO (carbon monoxide), oxides of sulphur etc.

CO reduces the lung capacity in humans while oxides of sulphur causes respiratory problems in humans and causes damage to buildings.

Answer: Option A. -> True
:
A

Dry cleaning and regular laundering are two different processes. Dry-cleaning does not use water while laundering does. In dry cleaning, chemical solvents are used to get rid of hard stains like pen ink. Most solvents used are extremely toxic. Clothes after dry cleaning release corrosive acidic fumes that can damage the lungs. Hence, we should air our newly dry-cleaned clothes to minimise contact with these harmful fumes.

Answer: Option D. -> Chlorofluorocarbons
:
D
Chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays are considered as pollutants. When CFCs escape into the atmosphere, they convert ozone$\left(O_3\right)$  to oxygen molecules$\left(O_2\right)$ and thus reduce the thickness of the ozone layer, which protects the Earth from the UV rays of the Sun.

Answer: Option D. -> Distillation
:
A, B, C, and D
There are many measures taken to make water fit for various purposes. Chlorination is a commonly used chemical method for purifying water. This is usually done by the municipality for household purposes. Similarly, filtration and boiling are also used for household purposes. Industrial laboratories require water that is completely free of dissolved salts. For this, most of the industries adopt the process of distillation as it is cheap and efficient.

Answer: Option D. -> Dirt
:
D

Filtration is a physical method to remove impurities. Some dissolved salts and minerals remain in water even after filtration. This is because salts, germs, minerals and some other substances can pass through a filter paper or filtering candle. 

Answer: Option C. -> Sulphuric acid
:
C and D
Acid rain mainly consists of sulphuric acid and nitric acid, as sulphur oxides and nitrogen oxides combines with water vapour to form sulphuric acid and nitric acid respectively.