Redox Reactions
74 Questions
Start JEE Mains Test
2021
Q51
JEE Mains
Numerical
14 Mar 2026
0.4 g mixture of NaOH, Na2CO3 and some inert impurities was first titrated with ${N \over {10}}$ HCl using phenolphthalein as an indicator, 17.5 mL of HCl was required at the end point. After this methyl orange was added and titrated. 1.5 mL of same HCl was required for the next end point. The weight percentage of Na2CO3 in the mixture is ________. (Rounded off to the nearest integer)
Correct Answer: 4
Explanation:
1st end point reaction :
$NaOH + HCl\buildrel {} \over \longrightarrow NaCl + {H_2}O$
$nf = 1$
$NaC{O_3} + HCl\buildrel {} \over \longrightarrow NaHC{O_3}$
$nf = 1$
Eq of HCl used $ = {n_{NaOH}} \times 1 + {n_{N{a_2}C{O_3}}} \times 1$
$17.5 \times {1 \over {10}} \times {10^{ - 3}} = {n_{NaOH}} + {n_{N{a_2}C{O_3}}}$
2nd end point :
$NaHC{O_3} + HCl\buildrel {} \over \longrightarrow {H_2}C{O_3}$
$1.5 \times {1 \over {10}} \times {10^{ - 3}} = {n_{NaHC{O_3}}} \times 1 = {n_{NaHC{O_3}}}$
0.15 mmol = ${n_{N{a_2}C{O_3}}}$
$0.15 = {n_{N{a_2}C{O_3}}}$
${w_{N{a_2}C{O_3}}} = {{0.15 \times 106 \times {{10}^{ - 3}}} \over {0.4}} \times 100 \times 10$
= 3.975%
$ \simeq $ 4%
$NaOH + HCl\buildrel {} \over \longrightarrow NaCl + {H_2}O$
$nf = 1$
$NaC{O_3} + HCl\buildrel {} \over \longrightarrow NaHC{O_3}$
$nf = 1$
Eq of HCl used $ = {n_{NaOH}} \times 1 + {n_{N{a_2}C{O_3}}} \times 1$
$17.5 \times {1 \over {10}} \times {10^{ - 3}} = {n_{NaOH}} + {n_{N{a_2}C{O_3}}}$
2nd end point :
$NaHC{O_3} + HCl\buildrel {} \over \longrightarrow {H_2}C{O_3}$
$1.5 \times {1 \over {10}} \times {10^{ - 3}} = {n_{NaHC{O_3}}} \times 1 = {n_{NaHC{O_3}}}$
0.15 mmol = ${n_{N{a_2}C{O_3}}}$
$0.15 = {n_{N{a_2}C{O_3}}}$
${w_{N{a_2}C{O_3}}} = {{0.15 \times 106 \times {{10}^{ - 3}}} \over {0.4}} \times 100 \times 10$
= 3.975%
$ \simeq $ 4%
2021
Q52
JEE Mains
MCQ
14 Mar 2026
The oxidation states of 'P' in H4P2O7, H4P2O5 and H4P2O6, respectively, are :
A.
7, 5 and 6
B.
5, 4 and 3
C.
5, 3 and 4
D.
6, 4 and 5
2021
Q53
JEE Mains
MCQ
14 Mar 2026
Identify the process in which change in the oxidation state is five :
A.
$C{r_2}O_7^{2 - } \to 2C{r^{3 + }}$
B.
$MnO_4^ - \to M{n^{2 + }}$
C.
$CrO_4^{2 - } \to C{r^{3 + }}$
D.
${C_2}O_4^{2 - } \to 2C{O_2}$
2021
Q54
JEE Mains
MCQ
14 Mar 2026
The oxidation states of nitrogen in NO, NO2, N2O and NO$_3^ - $ are in the order of :
A.
N2O > NO2 > NO > NO$_3^ - $
B.
NO > NO2 > N2O > NO$_3^ - $
C.
NO2 > NO$_3^ - $ > NO > N2O
D.
NO$_3^ - $ > NO2 > NO > N2O
2021
Q55
JEE Mains
MCQ
14 Mar 2026
Statement I : Sodium hydride can be used as an oxidising agent.
Statement II : The lone pair of electrons on nitrogen in pyridine makes it basic.
Choose the CORRECT answer from the options given below :
Statement II : The lone pair of electrons on nitrogen in pyridine makes it basic.
Choose the CORRECT answer from the options given below :
A.
Statement I is false but statement II is true
B.
Both statement I and statement II are true
C.
Statement I is true but statement II is false
D.
Both statement I and statement II are false
2020
Q56
JEE Mains
Numerical
14 Mar 2026
The volume, in mL, of 0.02 M K2Cr2O7 solution
required to react with 0.288 g of ferrous
oxalate in acidic medium is _______.
(Molar mass of Fe = 56 g mol–1)
(Molar mass of Fe = 56 g mol–1)
Correct Answer: 50
Explanation:
K2Cr2O7 + FeC2O4 $ \to $ Cr+3 + Fe+3 + CO2
nfactor of K2Cr2O7 = 3 $ \times $ 2 = 6
nfactor of FeC2O4 = 1 + 2 = 3
m. eq. of K2Cr2O7 = m. eq. of FeC2O4
$ \Rightarrow $ ${{6 \times 0.02 \times vol} \over {1000}}$ = ${{0.288} \over {144}} \times 3$
$ \Rightarrow $ vol = 50 ml
nfactor of K2Cr2O7 = 3 $ \times $ 2 = 6
nfactor of FeC2O4 = 1 + 2 = 3
m. eq. of K2Cr2O7 = m. eq. of FeC2O4
$ \Rightarrow $ ${{6 \times 0.02 \times vol} \over {1000}}$ = ${{0.288} \over {144}} \times 3$
$ \Rightarrow $ vol = 50 ml
2020
Q57
JEE Mains
Numerical
14 Mar 2026
A 100 mL solution was made by adding 1.43 g
of Na2CO3.xH2O. The normality of the solution
is 0.1 N. The value of x is _____.
(The atomic mass of Na is 23 g/mol)
(The atomic mass of Na is 23 g/mol)
Correct Answer: 10
Explanation:
Molar mass of Na2CO3.xH2O
= 23 × 2 + 12 + 48 + 18x
= 46 + 12 + 48 + 18x
= (106 + 18x)
As nfactor in dissolution will be determined from net cationic or anionic charge; which is 2
Eq wt = ${M \over 2}$ = (53 + 9x)
volume = 100 ml = 0.1 Litre
Normality =
$ \Rightarrow $ 0.1= ${{{{1.43} \over {53 + 9x}}} \over {0.1}}$
$ \Rightarrow $ 53 + 9x = 143
$ \Rightarrow $ 9x = 90
$ \Rightarrow $ x = 10
= 23 × 2 + 12 + 48 + 18x
= 46 + 12 + 48 + 18x
= (106 + 18x)
As nfactor in dissolution will be determined from net cationic or anionic charge; which is 2
Eq wt = ${M \over 2}$ = (53 + 9x)
volume = 100 ml = 0.1 Litre
Normality =
No. of equivalents of solute
Volume of solution (in L)
$ \Rightarrow $ 0.1= ${{{{1.43} \over {53 + 9x}}} \over {0.1}}$
$ \Rightarrow $ 53 + 9x = 143
$ \Rightarrow $ 9x = 90
$ \Rightarrow $ x = 10
2020
Q58
JEE Mains
Numerical
14 Mar 2026
The oxidation states of transition metal atoms
in K2Cr2O7, KMnO4 and K2FeO4, respectively,
are x, y and z. The sum of x, y and z is _______.
Correct Answer: 19
Explanation:
K2Cr2O7
Let oxidation state of Ce
2(+1) + 2x + 7(–2) = 0
$ \Rightarrow $ x = +6
In K2Cr2O7, Transition metal (Cr) present in +6 oxidation state.
KMnO4
(+1) + y + 4(–2) = 0
$ \Rightarrow $ x = +7
In KMnO4, transition metal (Mn) present in +7 oxidation state.
K2FeO4
2(+1) + z + 4(–2) = 0
$ \Rightarrow $x = +6
In K2FeO4, transition metal (Fe) present in +6 oxidation state.
$ \therefore $ x + y + z = 6 + 7 + 6 = 19
Let oxidation state of Ce
2(+1) + 2x + 7(–2) = 0
$ \Rightarrow $ x = +6
In K2Cr2O7, Transition metal (Cr) present in +6 oxidation state.
KMnO4
(+1) + y + 4(–2) = 0
$ \Rightarrow $ x = +7
In KMnO4, transition metal (Mn) present in +7 oxidation state.
K2FeO4
2(+1) + z + 4(–2) = 0
$ \Rightarrow $x = +6
In K2FeO4, transition metal (Fe) present in +6 oxidation state.
$ \therefore $ x + y + z = 6 + 7 + 6 = 19
2020
Q59
JEE Mains
MCQ
14 Mar 2026
While titrating dilute HCl solution with aqueous
NaOH, which of the following will not be
required?
A.
Pipette and distilled water
B.
Clamp and phenolphthalein
C.
Burette and porcelain tile
D.
Bunsen burner and measuring cylinder
2020
Q60
JEE Mains
MCQ
14 Mar 2026
The compound that cannot act both as oxidising
and reducing agent is :
A.
H3PO4
B.
H2SO3
C.
H2O2
D.
HNO2
2020
Q61
JEE Mains
MCQ
14 Mar 2026
The redox reaction among the following is :
A.
reaction of H2SO4 with NaOH.
B.
formation of ozone form atmosphere oxygen in the presence of sunlight.
C.
combination of dinitrogen with dioxygen at 2000 K
D.
reaction of [Co(H2O)6]Cl3 With AgNO3
2020
Q62
JEE Mains
MCQ
14 Mar 2026
Oxidation number of potassium in K2O. K2O2 and KO2 respectively is :
A.
+1, +2 and + 4
B.
+1, +1 and + 1
C.
+2, +1 and $ + {1 \over 2}$
D.
+1, +4, and +2
2019
Q63
JEE Mains
MCQ
14 Mar 2026
An example of a disproportionation reaction is :
A.
2NaBr + Cl2 $ \to $ 2NaCl + Br2
B.
2KMnO4 $ \to $ 2KMnO4 + MnO2 + O2
(3) (4)
C.
2CuBr $ \to $ CuBr2 + Cu
D.
2MnO4
+ 10I–
+ 16H+ $ \to $ 2Mn2+ + 5I2 + 8H2O
2019
Q64
JEE Mains
MCQ
14 Mar 2026
The correct order of the oxidation states of
nitrogen in NO, N2O, NO2 and N2O3 is :
A.
NO2 < NO < N2O3 < N2O
B.
NO2 < N2O3 < NO < N2O
C.
N2O < NO < N2O3 < NO2
D.
N2O < N2O3 < NO < NO2
2019
Q65
JEE Mains
MCQ
14 Mar 2026
In order to oxidise a mixture of one mole of each of FeC2O4, Fe2(C2O4)3, FeSO4 and Fe2(SO4)3 in
acidic medium, the number of moles of KMnO4 required is :
A.
1.5
B.
3
C.
2
D.
1
2019
Q66
JEE Mains
MCQ
14 Mar 2026
50 mL of 0.5 M oxalic acid is needed to neutralize 25 mL of sodium hydroxide solution. The amount of NaOH in 50 mL of the given sodium hydroxide solution is -
A.
20 g
B.
4 g
C.
80 g
D.
10 g
2019
Q67
JEE Mains
MCQ
14 Mar 2026
The hardness of a water sample (in terms of equivalents of CaCO3) containing 10–3 M CaSO4 is (Molar mass of CaSO4 = 136 g mol–1)
A.
90 ppm
B.
100 ppm
C.
50 ppm
D.
10 ppm
2019
Q68
JEE Mains
MCQ
14 Mar 2026
In the reaction of oxalate with permanganate in acidic medium, the number of electrons involved in producing one molecule of CO2 is :
A.
10
B.
2
C.
1
D.
5
2017
Q69
JEE Mains
MCQ
14 Mar 2026
Which of the following reactions is an example of a redox reaction?
A.
$Xe{F_6}$ + H2O $\to$ $XeO{F_4}$ + 2HF
B.
$Xe{F_6}$ + 2H2O $\to$ $XeO_2{F_2}$ + 4HF
C.
$Xe{F_4}$ + O2F2 $\to$ $Xe{F_6}$ + O2
D.
$Xe{F_2}$ + PF5 $\to$ ${\left[ {XeF} \right]^ + }PF_6^ - $
2016
Q70
JEE Mains
MCQ
14 Mar 2026
The volume of 0.1N dibasic acid sufficient to neutralize 1 g of a base that furnishes 0.04 mole of OH− in aqueous solution is :
A.
200 mL
B.
400 mL
C.
600 mL
D.
800 mL
2014
Q71
JEE Mains
MCQ
14 Mar 2026
In which of the following reactions H2O2 acts as a reducing agent?
1. H2O2 + 2H+ + 2e- $\to$ 2H2O
2. H2O2 - 2e- $\to$ O2 + 2H+
3. H2O2 + 2e- $\to$ 2OH-
4. H2O2 + 2OH- - 2e- $\to$ O2 + 2H2O
1. H2O2 + 2H+ + 2e- $\to$ 2H2O
2. H2O2 - 2e- $\to$ O2 + 2H+
3. H2O2 + 2e- $\to$ 2OH-
4. H2O2 + 2OH- - 2e- $\to$ O2 + 2H2O
A.
1, 2
B.
3, 4
C.
1, 3
D.
2, 4
2013
Q72
JEE Mains
MCQ
14 Mar 2026
Consider the following reaction:
$xMnO_4^- + yC_2O_4^{2-}$ + zH+ $\to$ xMn2+ + 2yCO2 + ${z \over 2}{H_2}O$
The value's of x, y and z in the reaction are, respectively :
$xMnO_4^- + yC_2O_4^{2-}$ + zH+ $\to$ xMn2+ + 2yCO2 + ${z \over 2}{H_2}O$
The value's of x, y and z in the reaction are, respectively :
A.
5, 2 and 16
B.
2, 5 and 8
C.
2, 5 and 16
D.
5, 2 and 8
2006
Q73
JEE Mains
MCQ
14 Mar 2026
Which of the following chemical reactions depicts the oxidizing behaviour of H2SO4?
A.
NaCl + H2SO4 $\to$ NaHSO4 + HCl
B.
2PCl5 + H2SO4 $\to$ 2POCl3 + 2HCl + SO2Cl2
C.
2HI + H2SO4 $\to$ I2 + SO2 + 2H2O
D.
Ca(OH)2 + H2SO4 $\to$ CaSO4 + 2H2O
2002
Q74
JEE Mains
MCQ
14 Mar 2026
Which of the following is a redox reaction ?
A.
NaCl + KNO3 $\to$ NaNO3 + KCl
B.
CaC2O4 + 2HCl $\to$ CaCl2 + H2C2O4
C.
Mg(OH)2 + 2NH4Cl $\to$ MgCl2 + 2NH4OH
D.
Zn + 2AgCN $\to$ 2Ag+ Zn(CN)2
