Pick the reaction or conversion that is (or is not) a redox change

1. A.
   Cr is reduced
2. B.
   Cr is oxidised
3. C.
   Oxidation number of Cr has neither decreased nor increased
4. D.
   Hydrogen is reduced

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1. A.
   $\text{Na} \rightarrow \text{Na}^+$
2. B.
   $\text{VO}^{2+} \rightarrow \text{V}_2\text{O}_3$
3. C.
   $\text{Zn}^{2+} \rightarrow \text{Zn}$
4. D.
   $\text{CrO}_4^{2-} \rightarrow \text{Cr}_2\text{O}_7^{2-}$

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1. A.
   $NaCl + {KNO}_{3} \longrightarrow {NaNO}_{3} + KCl$
2. B.
   $Mg(OH)_{2} + 2{NH}_{4}Cl \longrightarrow {MgCl}_{2} + 2{NH}_{4}OH$
3. C.
   $\ {CaC}_{2}O_{4} + 2HCl \longrightarrow {CaCl}_{2} + H_{2}C_{2}O_{4}$
4. D.
   $Zn + 2AgCN \longrightarrow 2Ag + Zn(CN)_{2}$

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1. A.
   $\mathrm{Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2}$
2. B.
   $\mathrm{Al(OH)_3 + 3HCl \rightarrow AlCl_3 + 3H_2O}$
3. C.
   $\mathrm{Mg + 1/2O_2 \rightarrow Mg^{2+} + O^{2-}}$
4. D.
   $\mathrm{Fe_{(s)} + Cu^{2+}_{(aq)} \rightarrow Fe^{2+}_{(aq)} + Cu_{(s)}}$

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1. A.
   $\mathrm{Cl_2 + 2H_2O + SO_2 \longrightarrow 4H^+ + SO_4^{2-} + 2Cl^-}$
2. B.
   $\mathrm{Cu^{2+} + Zn \longrightarrow Cu + Zn^{2+}}$
3. C.
   $\mathrm{2H_2 + O_2 \longrightarrow 2H_2O}$
4. D.
   $\mathrm{HCl + H_2O \longrightarrow H_3O^+ + Cl^-}$

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