Question
Which compound contains nitrogen with an oxidation number of +3?
A. NH4Cl
B. HNO3
C. N2O4
D. KNO2
▶️Answer/Explanation
D
NH4Cl, N +4-1 =0, N= -3.
HNO3 , N-6+1 =0, N=+5
N2O4 , 2N-8=0, N=+4
KNO2, N+1-4=0, N=+3
Question
Consider the following reaction.
\[{\text{MnO}}_4^ – ({\text{aq)}} + 8{{\text{H}}^ + }({\text{aq)}} + 5{\text{F}}{{\text{e}}^{2 + }}({\text{aq)}} \to {\text{M}}{{\text{n}}^{2 + }}{\text{(aq)}} + 5{\text{F}}{{\text{e}}^{3 + }}({\text{aq)}} + 4{{\text{H}}_{\text{2}}}{\text{O(l)}}\]
Which statement is correct?
A. \({\text{MnO}}_4^ – \) is the oxidizing agent and it loses electrons.
B. \({\text{MnO}}_4^ – \) is the reducing agent and it loses electrons.
C. \({\text{MnO}}_4^ – \) is the oxidizing agent and it gains electrons.
D. \({\text{MnO}}_4^ – \) is the reducing agent and it gains electrons.
▶️Answer/Explanation
C
In \({\text{MnO}}_4^ – \), Oxidation state of Mn = -1+8=+7.
It converts into Mn +2 oxidation state. Therefore, it gains electrons and gets reduced, hence, it is an oxidizing agent.
Question
The following equations indicate reactions that occur spontaneously.
\[\begin{array}{*{20}{l}} {{\text{Fe(s)}} + {\text{NiC}}{{\text{l}}_2}{\text{(aq)}} \to {\text{FeC}}{{\text{l}}_2}{\text{(aq)}} + {\text{Ni(s)}}} \\ {{\text{Zn(s)}} + {\text{FeC}}{{\text{l}}_2}{\text{(aq)}} \to {\text{ZnC}}{{\text{l}}_2}{\text{(aq)}} + {\text{Fe(s)}}} \\ {{\text{Ni(s)}} + {\text{PbC}}{{\text{l}}_2}{\text{(aq)}} \to {\text{NiC}}{{\text{l}}_2}{\text{(aq)}} + {\text{Pb(s)}}} \end{array}\]
Which is the increasing order of the reactivity of the metals?
A. \({\text{Fe}} < {\text{Ni}} < {\text{Zn}} < {\text{Pb}}\)
B. \({\text{Pb}} < {\text{Ni}} < {\text{Fe}} < {\text{Zn}}\)
C. \({\text{Ni}} < {\text{Zn}} < {\text{Pb}} < {\text{Fe}}\)
D. \({\text{Zn}} < {\text{Fe}} < {\text{Ni}} < {\text{Pb}}\)
▶️Answer/Explanation
B
A metal having more reactivity can displace another metal having less reactivity in a single displacement reaction.
Hence, here, Reactivity of Ni>Pb. Fe>Ni and Zn>Fe.
So, increasing order of reactivity is \({\text{Pb}} < {\text{Ni}} < {\text{Fe}} < {\text{Zn}}\).
Question
What is the correct order of reaction types in the following sequence?
▶️Answer/Explanation
A
Reaction I is substitution reaction as Br is substituted by OH.
Reaction II is oxidation of alcohol where it is converted into carboxylic acid.
Reaction III is condensation of carboxylic acid to form an ester.
Question
What is the name of \({\text{Mn}}{{\text{O}}_{\text{2}}}\)?
A. Manganese(II) oxide
B. Magnesium(II) oxide
C. Manganese(IV) oxide
D. Magnesium(IV) oxide
▶️Answer/Explanation
C
Oxidation state of Mn is Mn-4 =0, Mn = +4. Hence it is Manganese(IV) oxide.