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1

### JEE Main 2021 (Online) 27th August Morning Shift

The gas 'A' is having very low reactivity reaches to stratosphere. It is non-toxic and non-flammable but dissociated by UV-radiations in stratosphere. The intermediates formed initially from the gas 'A' are :
A
$$Cl\mathop O\limits^ \bullet + \mathop C\limits^ \bullet {F_2}Cl$$
B
$$Cl\mathop O\limits^ \bullet + C\mathop {{H_3}}\limits^ \bullet$$
C
$$\mathop C\limits^ \bullet {H_3} + C\mathop {{F_2}}\limits^ \bullet Cl$$
D
$$\mathop C\limits^ \bullet l + C\mathop {{F_2}}\limits^ \bullet Cl$$

## Explanation

In stratosphere CFCs get broken down by powerful UV radiations releasing $$C{l^ \bullet }$$

$$C{F_2}C{l_2}(g)\buildrel {U.V.} \over \longrightarrow C{l^ \bullet }(g) + {}^ \bullet C{F_2}Cl(g)$$
2

### JEE Main 2021 (Online) 26th August Evening Shift

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A) : Photochemical smog causes cracking of rubber.

Reason (R) : Presence of ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate in photochemical smog makes it oxidizing.

Choose the most appropriate answer from the options given below :
A
Both (A) and (R) are true but (R) is not the true explanation of (A)
B
(A) is false but (R) is true.
C
(A) is true but (R) is false.
D
Both (A) and (R) are true and (R) is the true explanation of (A)

## Explanation

Photochemical smog causes cracking of rubber, the common component of photochemical smog are ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyel nitrate (PAN).
3

### JEE Main 2021 (Online) 27th July Morning Shift

Which one of the following statements is NOT correct?
A
Eutrophication indicates that water body is polluted
B
The dissolved oxygen concentration below 6 ppm inhibits fish growth
C
Eutrophication leads to increase in the oxygen level in water
D

## Explanation

Eutrophication leads to decrease in oxygen level of water.

3rd statement is incorrect.
4

### JEE Main 2021 (Online) 25th July Evening Shift

Given below are two statements :

Statement I : Chlorofluoro breakdown by radiation in the visible energy region and release chlorine gas in the atmosphere which then reacts with stratospheric ozone.

Statement II : Atmospheric ozone reacts with nitric oxide to give nitrogen and oxygen gases, which add to the atmosphere.

For the above statements choose the correct answer from the options given below :
A
Statement I is incorrect but Statement II is true
B
Both Statement I and II are false
C
Statement I is correct but Statement II is false
D
Both Statement I and II are correct

## Explanation

Statement (1)

CFCs are broken down by powerful UV radiation and releases chlorine free radical which reacts with ozone and start chain reaction.

$$C{F_2}C{l_2}_{(g)}\buildrel {UV} \over \longrightarrow \mathop C\limits^ \bullet {l_g} + \mathop C\limits^ \bullet {F_2}C{l_{(g)}}$$

$$\mathop C\limits^ \bullet {l_{(g)}} + {O_{3(g)}} \to \mathop C\limits^ \bullet l{O_{(g)}} + {O_{2(g)}}$$

$$\mathop C\limits^ \bullet l{O_{(g)}} + {O_{(g)}} \to \mathop C\limits^ \bullet {l_{(g)}} + {O_{2(g)}}$$

Statement (2)

Atmosphere ozone reacts with nitric oxide to produce nitrogen dioxide and oxygen.

$$N{O_{(g)}} + {O_{3(g)}} \to N{O_{2(g)}} + {O_{2(g)}}$$

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