Environmental Chemistry — Page 7 | JEE Chemistry

Q61

The statement that is not true about ozone is :

A In the stratosphere, CFCs release chlorine free radicals (Cl) which reacts with O3 to give chlorine dioxide radicals

B It is a toxic gas and its reaction with NO gives NO2.

C In the atmosphere, it is depleted by CFCs

D In the stratosphere, it forms a protective shield against UV radiation

Correct Answer

Option A

Solution

In the stratosphere, CFCs release chlorine free radical (

\mathop {Cl}\limits^ \bullet

). CF2Cl2(g)

\overset{{UV}}\longrightarrow

\mathop {Cl}\limits^ \bullet

(g) +

\mathop {Cl}\limits^ \bullet

F2Cl(g) Which react with O3 to give chlorine oxide (Cl

\mathop O\limits^ \bullet

) radical not chlorine dioxide (Cl

\mathop O\limits^ \bullet

2) radical.

\mathop {Cl}\limits^ \bullet

(g) + O3(g) $\to$ Cl

\mathop O\limits^ \bullet

(g) + O2(g)

Q62

Identify the pollutant gases largely responsible for the discoloured and lustreless nature of marble of the Taj Mahal.

A O3 and CO2

B CO2 and NO2

C SO2 and NO2

D SO2 and O3

Correct Answer

Option C

Solution

SO2 and NO2 are responsible for the discoloured and lustreless nature of marble.

Q63

The deposition of X and Y on ground surfaces is referred as wet and dry depositions, respectively. X and Y are :

A X = Ammonium salts, Y = CO2

B X = SO2, Y = Ammonium salts

C X = Ammonium salts, Y = SO2

D X = CO2, Y = SO2

Correct Answer

Option C

Solution

Oxides of nitrogen and sulphur are acidic and settle down on ground as dry deposition.

Ammonium salts in rain drops result in wet deposition.

Q64

In stratosphere most of the ozone formation is assisted by :

A cosmic rays

B

\gamma

-rays

C ultraviolet radiation

D visible radiations

Correct Answer

Option C

Solution

Ozone in the stratosphere is a product of UV radiations acting on dioxygen (O2) molecules.

{O_2}(g)\overset{{UV}}\longrightarrow O(g) + O(g)

O(g) + {O_2}(g)

\overset{{UV}}\rightleftharpoons

{O_3}(g)

Q65

The primary pollutant that leads to photochemical smog is :

A acrolein

B ozone

C sulphur dioxide

D nitrogen oxides

Correct Answer

Option D

Solution

Photochemical smog contains oxides of nitrogen.

Q66

The layer of atmosphere between 10 km to 50 km above the sea level is called as :

A mesosphere

B thermosphere

C troposphere

D stratosphere

Correct Answer

Option D

Solution

Between 10-50 km above sea level is the lowest level which is called stratosphere.

Q67

The presence of ozone in troposphere :

A protects us from greenhouse effect

B protects us from the UV radiation

C protects us from the X-ray radiation

D generates photochemical smog

Correct Answer

Option D

Solution

Ozone is a strong oxidising agent like NO2.

In troposphere both O3 and NO2 react with the unburnt hydrocarbons to produce the chemical components of photochemical smog, like formaldehyde (HCHO), acrolein (CH2 = CH - CHO) and PAN or peroxyacetyl nitrate.

Hence, in troposphere, the presence of ozone generates photochemical smog.

Q68

A water sample has ppm level concentration of following anions F- = 10;

SO_4^{2-}

= 100;

NO_3^-

= 50 The anion/anions that make/makes the water sample unsuitable for drinking is/are :

A both

SO_4^{2-}

and

NO_3^-

B only F-

C only

SO_4^{2-}

D only

NO_3^-

Correct Answer

Option B

Solution

Permissible limit for SO4 2- = 500 ppm Permissible limit for NO3 - = 50 ppm Permissible limit for F- = 1 ppm

Q69

Given below are two statements : Statement I : The value of the parameter "Biochemical Oxygen Demand (BOD)" is important for survival of aquatic life. Statement II : The optimum value of BOD is 6.5 ppm. In the light of the above statements, choose the most appropriate answer from the options given below :

A Statement I is false but Statement II is true

B Statement I is true but Statement II is false

C Both Statement I and Statement II are true

D Both Statement I and Statement II are false

Correct Answer

Option B

Solution

Clean water would have BOD value of less than 5 ppm whereas highly polluted water could have a BOD value of 17 ppm or more.

Hence, the value of parameter ‘BOD’ is important for survival of aquatic life but optimum value of BOD is 17 ppm or more.

So, statement II is incorrect.

Q70

Some gases are responsible for heating of atmosphere (green house effect). Identify from the following the gaseous species which does not cause it.

A CH4

B O3

C H2O

D N2

Correct Answer

Option D

Solution

Among the given gases, the green house gases which are responsible for heating the atmosphere are CH4, water vapour and ozone.

Nitrogen is not a green house gas.