Question

which one of the following reactions is a redox reaction? none of these pb + 2cl → pbcl₂ agno₃ + hcl → hno₃ + agcl naoh + hcl → nacl + h₂o

Explanation:

Step1: Define redox reaction

A redox reaction involves changes in oxidation numbers of elements (electron transfer).

Step2: Analyze Reaction 1: $\text{Pb} + 2\text{Cl}

ightarrow \text{PbCl}_2$

• Oxidation number of $\text{Pb}$: $0

ightarrow +2$ (oxidized, loses electrons)

• Oxidation number of $\text{Cl}$: $0

ightarrow -1$ (reduced, gains electrons)

Step3: Analyze Reaction 2: $\text{AgNO}_3 + \text{HCl}

ightarrow \text{HNO}_3 + \text{AgCl}$
All elements have unchanged oxidation numbers: $\text{Ag}=+1$, $\text{N}=+5$, $\text{O}=-2$, $\text{H}=+1$, $\text{Cl}=-1$. This is a double displacement reaction, not redox.

Step4: Analyze Reaction 3: $\text{NaOH} + \text{HCl}

ightarrow \text{NaCl} + \text{H}_2\text{O}$
All elements have unchanged oxidation numbers: $\text{Na}=+1$, $\text{O}=-2$, $\text{H}=+1$, $\text{Cl}=-1$. This is a neutralization reaction, not redox.

Answer:

Pb + 2Cl → PbCl₂