NEW
New Website Launch
Experience the best way to solve previous year questions with mock tests (very detailed analysis), bookmark your favourite questions, practice etc...
1

### NEET 2020 Phase 1

What is the change in oxidation number of carbon in the following reaction?
CH4(g) + 4Cl2(g) $$\to$$ CCl4(l) + 4HCl(g)
A
0 to + 4
B
$$-$$4 to + 4
C
0 to $$-$$ 4
D
+ 4 to + 4

## Explanation Change in oxidation state of carbon is from $$-$$ 4 to + 4
2

### NEET 2019

Which of the following reactions are disproportionation reaction?

(a) 2Cu+ $$\to$$ Cu2+ + Cu0
(b) 3MnO42+ + 4H+ $$\to$$ 2MnO4- + MnO2 + 2H2O
(c) 2KMnO4 $$\buildrel \Delta \over \longrightarrow$$ K2MnO4 + MnO2 + O2
(d) 2MnO4- + 3Mn2+ + 2H2O $$\to$$ 5MnO2 + 4$${H^ \oplus }$$

Select the correct option from the following :
A
(a), (c) and (d)
B
(a) and (b) only
C
(a) and (d) only
D
(a), (b) and (c)

## Explanation

In a disproportionation reaction, same substance undergoes oxidation (increase in oxidation number) and reduction (decrease in oxidation number forming two different products. 3

### NEET 2018

The correct order of N-compounds in its decreasing order of oxidation states is
A
HNO3 , NO, N2 , NH4Cl
B
HNO3 , NO, NH4Cl, N2
C
HNO3 , NH4Cl, NO, N
D
NH4Cl, N2 , NO, HNO3

## Explanation

$$H\mathop N\limits^{ + 5} {O_3},\mathop N\limits^{ + 2} O,\mathop {{N_2}}\limits^0 ,\mathop N\limits^{ - 3} {H_4}Cl$$
4

### NEET 2018

Consider the change in oxidation state of bromine corresponding to different emf values as shown in the given diagram : Then the species undergoing disproportionation is :
A
BrO4
B
BrO3
C
Br2
D
HBrO

## Explanation

Calculate Eocell corresponding to each compound undergoing disproportionation reaction. The reaction for which Eocell comes out + ve is spontaneous.

HBrO $$\to$$ Br2, EoHBrO/Br2 = 1.595 V

HBrO $$\to$$ BrO3, EoBrO3-/HBrO = 1.595 V

Eocell for the disproportionation of HBrO,

Eocell = EoHBrO/Br2 - EoBrO3-/HBrO

= 1.595 - 1.5

= 0.095 V = + ve

So, Eocell > 0

So, $$\Delta$$Go < 0 (Spontaneous)

#### Questions Asked from Redox Reactions

On those following papers in MCQ (Single Correct Answer)
Number in Brackets after Paper Indicates No. of Questions
NEET 2020 Phase 1 (1)
NEET 2019 (1)
NEET 2018 (3)
NEET 2016 Phase 2 (1)
AIPMT 2014 (3)
AIPMT 2012 Prelims (2)
AIPMT 2009 (1)
AIPMT 2008 (1)
AIPMT 2004 (1)
AIPMT 2003 (1)

### Joint Entrance Examination

JEE Main JEE Advanced WB JEE

### Graduate Aptitude Test in Engineering

GATE CSE GATE ECE GATE EE GATE ME GATE CE GATE PI GATE IN

NEET

Class 12