1
MCQ (Single Correct Answer)

### JEE Main 2019 (Online) 9th January Morning Slot

A water sample has ppm level concentration of the following metals : Fe = 0.2; Mn = 5.0; Cu = 3.0; Zn = 5.0. The metal that makes the water sample unsuitable for drinking is :
A
Cu
B
Mn
C
Fe
D
Zn

## Explanation

When Mn present in water with concentration 0.05 ppm or more than this then the water is unsuitable for drinking.

Here given concentration for Mn is 5.0, which is grater than 0.05 that is why it is Mn makes water unsuitable for drinking.

For other metal water is suitable for drinking when concentration for Fe = 0.2 ppm and for Cu = 3.0 ppm and for Zn = 5.0 ppm.
2
MCQ (Single Correct Answer)

### JEE Main 2019 (Online) 9th January Evening Slot

Which of the following conditions in drinking water causes methemoglobinemia ?
A
> 50 ppm of lead
B
> 50 ppm of chloride
C
> 50 ppm of nitrate
D
> 100 ppm of sulphate

## Explanation

Concentration of nitrate > 50 ppm in drinking water causes methemoglobinemia
3
MCQ (Single Correct Answer)

### JEE Main 2019 (Online) 10th January Morning Slot

Water filled in two glasses A and B have BOD values of 10 and 20, respectively. The correct statement regarding them, is
A
B is more polluted than A.
B
A is suitable for drinking, whereas B is not .
C
Both A and B are suitable for dirnking
D
A is more polluted than B.

## Explanation

Two glasses ''A'' and ''B'' have BOD values 10 and ''20'', respectively.

Hence glasses ''B'' is more polluted than glasses ''A''.
4
MCQ (Single Correct Answer)

### JEE Main 2019 (Online) 10th January Evening Slot

The reaction that is NOT involved in the ozone layer depletion mechanism in the stratosphere is :
A
$Cl\mathop O\limits^ \bullet \left( g \right) + O\left( g \right) \to \mathop C\limits^ \bullet l\left( g \right) + {O_2}(g)$
B
$C{F_2}C{l_2}\left( g \right)\,\buildrel {uv} \over \longrightarrow \mathop {\,C}\limits^ \bullet l\left( g \right) + \mathop C\limits^ \bullet {F_2}Cl\left( g \right)$
C
$C{H_4} + 2{O_3}\, \to \,3C{H_2} = O + 3{H_2}O$
D
$HOCl\left( g \right)\,\buildrel {hv} \over \longrightarrow \,\mathop O\limits^ \bullet H\left( g \right) + \mathop C\limits^ \bullet l\left( g \right)$

## Explanation

Ozone layer depletion mechanism occurs with Chlorofluorocarbons and involves chlorine radical.

In CH4, there is no Cl so it is not involved in the ozone layer depletion mechanism

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