Environmental chemistry

This is a Assertion Type Questions as classified in NCERT Exemplar

Option (ii)

 i.e., Both A and R are correct, but R is not the correct explanation of A is the answer the pH of rainwater is 5.6 because of the presence of hydronium ions produced due to the dissolution of carbon dioxide in rainwater from atmosphere and when the pH of rainwater drops from 5.6, it is being referred as acid rain. This can be shown as-

H₂O (l)+CO₂ (g)→H₂CO₃ (aq)

H₂CO₃ (aq)→H+ (aq)+HCO₃⁻ (aq)

This is a Assertion Type Questions as classified in NCERT Exemplar

Option (iii)

i.e., Both A and R are not correct is the answer since in cold places, sunlight required to grow plants is less. Due to which plants are kept in a glass house so that sunlight enters in the greenhouse to heat up the soil and plants. The warm soil and plants emit infrared radiations which are partially absorbed and partially reflected by the glass. 

This is a Short answer type Questions as classified in NCERT Exemplar

Excessive amount of sulphate (i.e., greater than 500 ppm) in drinking water causes laxative effect, otherwise at moderate levels it is harmless.

This is a Short answer type Questions as classified in NCERT Exemplar

Ozone is found to be thermodynamically unstable and undergoes decomposition into molecular oxygen and a dynamic equilibrium exists between the production and decomposition of ozone. The reactions involved can be shown as- 

O₂ (g)  O (g) + O (g)

O (g) + O₂ (g) +M O₃ (g) + M

This is a  Short Answers Type Questions as classified in NCERT Exemplar

Ozone in the stratosphere is formed when UV radiation falls on the dioxygen (O₂ ) molecules. The UV radiations split apart molecular oxygen into free oxygen (O) atoms, these oxygen atoms combine with molecular oxygen to form ozone. The reactions involved can be given as-

O₂ (g)  O (g) + O (g)

O (g) + O₂ (g) +M O₃ (g) + M

This is a  Short Answers Type Questions as classified in NCERT Exemplar

NO₂ absorbs energy from sunlight and breaks up into nitric oxide and free oxygen atom and this can be shown as- 

NO₂ (g) NO (g)+O (g)

Here the oxygen atom produced is very reactive and combines with oxygen molecule in the air to give rise to ozone. 

O (g) +O₂ (g) + M → O₃ (g) + M

Here 'M' is an inert gas like Nitrogen gas and ozone gets produced during the formation of smog.

This is a  Short Answers Type Questions as classified in NCERT Exemplar

The uncatalyzed oxidation of SO₂ is a slow process. However, the presence of particulate matter in the polluted air catalyses the oxidation of SO₂ to SO₃. The reaction for the conversion can be given as-

2SO₂ (g)+O₂ (g)→2SO₃ (g)

The reaction can be promoted by O3 or by H₂O₂.

SO₂ (g)+O₃ (g)→2SO₃ (g)+O₂ (g)

SO₂ (g)+H₂O₂ (l)→H2SO₄ (aq)

This is a  Short Answers Type Questions as classified in NCERT Exemplar

The symptoms which were observed in  the village indicate that oxides of sulphur and nitrogen are released from the chimneys of the factory. These gases are obtained as the product of combustion of fossil fuels such as coal,   gasoline etc. In an automobile engine, at high temperature, when fossil fuel is burnt, dinitrogen and dioxygen get combined to give significant quantities of nitric oxide and nitrogen dioxide. The chemical reactions can be given as-

This is a  Short Answers Type Questions as classified in NCERT Exemplar

Due to the excessive growth of algae water contains a lot of phosphate due to the inflow of the fertilizers from the surroundings. The decomposition of algae leads to the bad smell and taste and even makes it unfit for  drinking, bathing, washing, swimming, boating etc. and concentration of dissolved oxygen also decreases which may be harmful for aquatic life.