Redox Reactions · JEE Main previous year questions

An example of a disproportionation reaction is :

1. A.$2\text{NaBr}+{\text{Cl}}_2\to 2\text{NaCl}+{\text{Br}}_2$
2. B.$2{\text{KMnO}}_4\to {\text{K}}_2{\text{MnO}}_4+{\text{MnO}}_2+{\text{O}}_2$
3. C.$2\text{CuBr}\to {\text{CuBr}}_2+\text{Cu}$
4. D.$2{\text{MnO}}_4^{-}+10{\text{I}}^{-}+16{\text{H}}^{+}\to 2{\text{Mn}}^{2+}+5{\text{I}}_2+8{\text{H}}_2\text{O}$

The highest possible oxidation states of uranium and plutonium, respectively are :

1. A.4 and 6
2. B.6 and 4
3. C.7 and 6
4. D.6 and 7

The correct order of the oxidation states of nitrogen in NO, ${\mathrm{N}}_2\mathrm{O}$, $\mathrm{N}{\mathrm{O}}_2$ and ${\mathrm{N}}_2{\mathrm{O}}_3$ is :

1. A.$\mathrm{N}{\mathrm{O}}_2<\mathrm{NO}<{\mathrm{N}}_2{\mathrm{O}}_3<{\mathrm{N}}_2\mathrm{O}$
2. B.$\mathrm{N}{\mathrm{O}}_2<{\mathrm{N}}_2{\mathrm{O}}_3<\mathrm{NO}<{\mathrm{N}}_2\mathrm{O}$
3. C.${\mathrm{N}}_2\mathrm{O}<\mathrm{NO}<{\mathrm{N}}_2{\mathrm{O}}_3<\mathrm{N}{\mathrm{O}}_2$
4. D.${\mathrm{N}}_2\mathrm{O}<{\mathrm{N}}_2{\mathrm{O}}_3<\mathrm{NO}<\mathrm{N}{\mathrm{O}}_2$

The maximum number of possible oxidation states of actinoides are shown by :

1. A.nobelium (No) and lawrencium (Lr)
2. B.actinium (Ac) and thorium (Th)
3. C.neptunium (Np) and plutonium (Pu)
4. D.berkelium (Bk) and californium (Cf)

Iodine reacts with concentrated $\mathrm{HN}{\mathrm{O}}_3$ to yield Y along with other products. The oxidation state of iodine in Y, is :

1. A.3
2. B.1
3. C.7
4. D.5

The relative stability of +1 oxidation state of group 13 elements follows the order :

1. A.Tl < In < Ga < Al
2. B.Al < Ga < Tl < In
3. C.Al < Ga < In < Tl
4. D.Ga < Al < In < Tl

Aluminium is usually found in +3 oxidation state. In contrast, thallium exists in + 1 and + 3 oxidation states. This is due to :

1. A.inert pair effect
2. B.diagonal relationship
3. C.lattice structure
4. D.lanthanoid contraction

When $\mathrm{X}{\mathrm{O}}_2$ is fused with an alkali metal hydroxide in presence of an oxidizing agent such as $\mathrm{KN}{\mathrm{O}}_3$ ; a dark green product is formed which disproportionates in acidic solution to afford a dark purple solution. $\mathrm{X}$ is :

1. A.$\mathrm{Ti}$
2. B.$\mathrm{V}$
3. C.$\mathrm{Cr}$
4. D.$\mathrm{Mn}$

The oxidation states of Cr in $[\text{Cr}({\text{H}}_2\text{O}{)}_6]{\text{Cl}}_3$, $[\text{Cr}({\text{C}}_6{\text{H}}_6{)}_2]$ and ${\text{K}}_2[\text{Cr}(\text{CN}{)}_2(\text{O}{)}_2({\text{O}}_2)({\text{NH}}_3)]$ respectively are :

1. A.+3, 0 and +4
2. B.+3, +4 and +6
3. C.+3, +2 and +4
4. D.+3, 0 and +6

The number of P–OH bonds and the oxidation state of phosphorus atom in pyrophosphoric acid (${\mathrm{H}}_4{\mathrm{P}}_2{\mathrm{O}}_7$) respectively are :

1. A.four and four
2. B.five and four
3. C.five and five
4. D.four and five

The pair of compounds having metals in their highest oxidation state is :

1. A.$\mathrm{M}{\mathrm{n}}_2{\mathrm{O}}_7$ and $\mathrm{Cr}{\mathrm{O}}_2\mathrm{C}{\mathrm{l}}_2$
2. B.$[\mathrm{NiC}{\mathrm{l}}_4{]}^{2-}$ and $[\mathrm{CoC}{\mathrm{l}}_4{]}^{2-}$
3. C.$[\mathrm{Fe}(\mathrm{CN}{)}_6{]}^{3-}$ and $[\mathrm{Cu}(\mathrm{CN}{)}_4{]}^{2-}$
4. D.$[\mathrm{FeC}{\mathrm{l}}_4{]}^{-}$ and $\mathrm{C}{\mathrm{o}}_2{\mathrm{O}}_3$

In which of the following reactions, hydrogen peroxide acts as an oxidizing agent ?

1. A.$\mathrm{HOCl}+{\mathrm{H}}_2{\mathrm{O}}_2\to {\mathrm{H}}_3{\mathrm{O}}^{+}+\mathrm{C}{\mathrm{l}}^{-}+{\mathrm{O}}_2$
2. B.${\mathrm{I}}_2+{\mathrm{H}}_2{\mathrm{O}}_2+2O{\mathrm{H}}^{-}\to 2{\mathrm{I}}^{-}+2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2$
3. C.$2\mathrm{Mn}{\mathrm{O}}_4^{-}+3{\mathrm{H}}_2{\mathrm{O}}_2\to 2\mathrm{Mn}{\mathrm{O}}_2+3{\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}+2\mathrm{O}{\mathrm{H}}^{-}$
4. D.$\mathrm{PbS}+4{\mathrm{H}}_2{\mathrm{O}}_2\to \mathrm{PbS}{\mathrm{O}}_4+4{\mathrm{H}}_2\mathrm{O}$

The pair in which phosphorous atoms have a formal oxidation state of +3 is :

1. A.Orthophosphorous and pyrophosphorous acids
2. B.Pyrophosphorous and hypophosphoric acids
3. C.Orthophosphorus and hypophosphoric acids
4. D.Pyrophosphorous and pyrophosphoric acids

In which of the following reactions ${\mathrm{H}}_2{\mathrm{O}}_2$ acts as a reducing agent? 1. ${\mathrm{H}}_2{\mathrm{O}}_2+2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to 2{\mathrm{H}}_2\mathrm{O}$ 2. ${\mathrm{H}}_2{\mathrm{O}}_2-2{\mathrm{e}}^{-}\to {\mathrm{O}}_2+2{\mathrm{H}}^{+}$ 3. ${\mathrm{H}}_2{\mathrm{O}}_2+2{\mathrm{e}}^{-}\to 2O{\mathrm{H}}^{-}$ 4. ${\mathrm{H}}_2{\mathrm{O}}_2+2O{\mathrm{H}}^{-}-2{\mathrm{e}}^{-}\to {\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}$

1. A.1, 2
2. B.3, 4
3. C.1, 3
4. D.2, 4

Which of the following forms stable $+4$ oxidation state?

1. A.$\mathrm{La}(Z=57)$
2. B.$\mathrm{Eu}(Z=63)$
3. C.$\mathrm{Ce}(Z=58)$
4. D.$\mathrm{Gd}(Z=64)$

In the following balanced reaction, $X\mathrm{Mn}{\mathrm{O}}_4^{-}+Y{\mathrm{C}}_2{\mathrm{O}}_4^{2-}+Z{\mathrm{H}}^{+}\rightleftharpoons X\mathrm{M}{\mathrm{n}}^{2+}+2Y\mathrm{C}{\mathrm{O}}_2+\frac{Z}{2}{\mathrm{H}}_2\mathrm{O}$ values of $X,Y$ and $Z$ respectively are

1. A.$2,5,16$
2. B.$8,2,5$
3. C.$5,2,16$
4. D.$5,8,4$

Knowing that the Chemistry of lanthanoids (Ln) is dominated by its +3 oxidation state, which of the following statements is incorrect?

1. A.Because of the large size of the Ln (III) ions the bonding in its compounds is predominantly ionic in character.
2. B.The ionic sizes of Ln (III) decrease in general with increasing atomic number.
3. C.Ln (III) compounds are generally colourless
4. D.Ln (III) hydroxides are mainly basic in character.

A metal, $M$ forms chlorides in its $+2$ and $+4$ oxidation states. Which of the following statements about these chlorides is correct?

1. A.$M\mathrm{C}{\mathrm{l}}_2$ is more ionic than $M\mathrm{C}{\mathrm{l}}_4$
2. B.$M\mathrm{C}{\mathrm{l}}_2$ is more easily hydrolysed than $M\mathrm{C}{\mathrm{l}}_4$
3. C.$M\mathrm{C}{\mathrm{l}}_2$ is more volatile than $M\mathrm{C}{\mathrm{l}}_4$
4. D.$M\mathrm{C}{\mathrm{l}}_2$ is more soluble in anhydrous ethanol than $M\mathrm{C}{\mathrm{l}}_4$.

What products are expected from the disproportionation reaction of hypochlorous acid?

1. A.$\mathrm{HCl}{\mathrm{O}}_3$ and $\mathrm{C}{\mathrm{l}}_2\mathrm{O}$
2. B.$\mathrm{HCl}{\mathrm{O}}_2$ and $\mathrm{HCl}{\mathrm{O}}_4$
3. C.$\mathrm{HCl}$ and $\mathrm{C}{\mathrm{l}}_2\mathrm{O}$
4. D.$\mathrm{HCl}$ and $\mathrm{HCl}{\mathrm{O}}_3$

The oxidation state of $\mathrm{Cr}$ in $[\mathrm{Cr}(\mathrm{N}{\mathrm{H}}_3{)}_4\mathrm{C}{\mathrm{l}}_2{]}^{+}$ is :

1. A.$+3$
2. B.$+2$
3. C.$+1$
4. D.$0$

The $E_{M^{3+}/M^{2+}}^{\circ }$ values for Cr, Mn, Fe and Co are – 0.41, +1.57, + 0.77 and +1.97 V respectively. For which one of these metals the change in oxidation state from +2 to +3 is easiest?

1. A.Fe
2. B.Mn
3. C.Cr
4. D.Co

Which of the following is a redox reaction ?

1. A.$\mathrm{NaCl}+\mathrm{KN}{\mathrm{O}}_3\to \mathrm{NaN}{\mathrm{O}}_3+\mathrm{KCl}$
2. B.$\mathrm{Ca}{\mathrm{C}}_2{\mathrm{O}}_4+2HCl\to \mathrm{CaC}{\mathrm{l}}_2+{\mathrm{H}}_2{\mathrm{C}}_2{\mathrm{O}}_4$
3. C.$\mathrm{Mg}(\mathrm{OH}{)}_2+2N{\mathrm{H}}_4\mathrm{Cl}\to \mathrm{MgC}{\mathrm{l}}_2+2N{\mathrm{H}}_4\mathrm{OH}$
4. D.$\mathrm{Zn}+2AgCN\to 2Ag+\mathrm{Zn}(\mathrm{CN}{)}_2$

Oxidation number of Cl in $\mathrm{CaOC}{\mathrm{l}}_2$ (bleaching powder) is :

1. A.zero, since it contains $\mathrm{C}{\mathrm{l}}_2$
2. B.-1, since it contains $\mathrm{C}{\mathrm{l}}^{-}$
3. C.+1, since it contains $\mathrm{Cl}{\mathrm{O}}^{-}$
4. D.+1 and -1 since it contains $\mathrm{Cl}{\mathrm{O}}^{-}$ and $\mathrm{C}{\mathrm{l}}^{-}$

When $\mathrm{KMn}{\mathrm{O}}_4$ acts as an oxidising agent and ultimately forms $[\mathrm{Mn}{\mathrm{O}}_4{]}^{-2},\mathrm{Mn}{\mathrm{O}}_2,\mathrm{M}{\mathrm{n}}_2{\mathrm{O}}_3,\mathrm{M}{\mathrm{n}}^{+2}$ then the number of electrons transferred in each case respectively is :

1. A.4, 3, 1, 5
2. B.1, 5, 3, 7
3. C.1, 3, 4, 5
4. D.3, 5, 7, 1

Most common oxidation states of Ce (cerium) are :

1. A.+3, +4
2. B.+2, +3
3. C.+2, +4
4. D.+3, +5