Environmental Chemistry

Option A is not true about photochemical smog.

Explanation:

• Photochemical smog is harmful to both humans and plants. It damages plant tissues and affects their growth.

• Option A says: "Photochemical smog is harmful to humans but has no effect on plants." This is incorrect because it does affect plants.

Other options:

• Option B: Plants like Pinus, Juniparus can reduce photochemical smog — This is correct.

• Option C: Photochemical smog occurs in warm, dry and sunny climate — This is correct.

• Option D: Common components include ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate — This is correct.

Final Answer:

Option A

The correct answer is Option C : Statement I is incorrect but Statement II is true.

Statement I is incorrect. Eutrophication is not caused by nutrient-deficient water bodies, but rather by nutrient-rich water bodies. This process typically occurs when a body of water becomes overly enriched with nutrients (like phosphates and nitrates), often due to runoff from the land, which causes a dense growth of plant life, particularly algae blooms.

Statement II is true. The excessive plant growth and algal blooms caused by eutrophication can deplete the oxygen levels in the water when these organisms die and decompose. This can lead to the death of animal life, particularly fish, in the affected water body, a condition known as hypoxia.

	List-I		List-II
(a)	Biochemical oxygen demand	(i)	organic matter in water
(b)	Photochemical smog	(ii)	oxidising mixture
(c)	Classical smog	(iii)	reducing mixture
(d)	Ozone layer depletion	(iv)	polar stratospheric cloud

(a) - (iii), (b) - (i), (c) - (iv), (d) - (ii)

$\bullet$ Tropospheric pollution : In the presence of pollutant, SO₂ converts into SO₃.

$2S{O_2} + {O_2} \to 2S{O_3}$

$\bullet$ In spring season, sunlight breaks HOCl and Cl₂ to give chlorine radicals.

$HOCl\buildrel {hv} \over \longrightarrow \mathop O\limits^ \bullet H(g) + \mathop C\limits^ \bullet l(g)$

These chlorine radicals deplete ozone layer

$\bullet$ High level of sulphur causes acid rain which reacts with marble and causes discolouring and disfiguring

$CaC{O_3} + {H_2}S{O_4} \to CaS{O_4} + {H_2}O + C{O_2}$

$\bullet$ A chain reaction occurs from interaction of NO with sunlight in which NO is converted to NO₂ which absorb energy from sunlight and breaks into NO and O, which causes photochemical smog.

$N{O_2}(g)\buildrel {hv} \over \longrightarrow NO(g) + O(g)$

Sulphurdioxide (SO₂) is not a green house gas.

N₂O₅ is highest oxidation number oxide which will not easily formed by common or natural oxidation of lower oxides of nitrogen.

CFC (Chlorofluoro carbons) is not the component of photochemical smog.

Acid rain is the rain water containing sulphuric acid and nitric acid which are formed from the oxides of sulphur and nitrogen present in the air as pollutants and rain water has a pH range of 4-5.

Photochemical smog cause eye and throat irritation.

Fish dies in water bodies polluted by sewage due to decrease in dissolved oxygen (DO).

Green chemistry may be defined as the programme of developing new chemical products and chemical processes or making improvements in the already existing compounds and processes so as to make them less harmful to human health and environment. This means the same as to reduce the use and production of hazardous chemicals.

Microorganisms present in the soil is a sink for CO.

Both assertion and reason are correct but reason is not the correct explanation of assertion. Normally, rain water has a pH of 5.6 due to the presence of H$^+$ ions formed by the reaction of rain water with carbon dioxide present in the atmosphere.

$\mathrm{H}_2 \mathrm{O}(l)+\mathrm{CO}_2(g) \longrightarrow \mathrm{H}_2 \mathrm{CO}_3(a q)$

$\mathrm{H}_2 \mathrm{CO}_3(a q) \rightleftharpoons \mathrm{H}^{+}(a q)+\mathrm{HCO}_3^{-}(a q)$

When the $\mathrm{pH}$ of rain water drops below 5.6, it is called acid rain.