Which balanced equation represents a redox reaction? $\newline$ ( $1$ ) $\mathrm{AgNO}_{3(\mathrm{aq})}+\mathrm{NaCl}_{(\mathrm{aq})} \rightarrow \mathrm{AgCl}_{(\mathrm{s})}+\mathrm{NaNO}_{3(\mathrm{aq})}$ $\newline$ ( $2$ ) $\mathrm{H}_{2} \mathrm{CO}_{3(\mathrm{aq})} \rightarrow \mathrm{H}_{2} \mathrm{O}_{(\ell)}+\mathrm{CO}_{2(\mathrm{~g})}$ $\newline$ ( $3$ ) $\mathrm{NaOH}_{(\mathrm{aq})}+\mathrm{HCl}_{(\mathrm{aq})} \rightarrow \mathrm{NaCl}_{(\mathrm{aq})}+\mathrm{H}_{2} \mathrm{O}_{(\ell)}$ $\newline$ ( $4$ ) $\mathrm{Mg}_{\text {(s) }}+2 \mathrm{HCl}_{\text {(aq) }} \rightarrow \mathrm{MgCl}_{\text {(aq) }}+\mathrm{H}_{2(\mathrm{~g})}$ $\newline$ $1$ $\newline$ $2$ $\newline$ $3$ $\newline$ $4$

Full solution

Q. Which balanced equation represents a redox reaction?

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(

1

)

\mathrm{AgNO}_{3(\mathrm{aq})}+\mathrm{NaCl}_{(\mathrm{aq})} \rightarrow \mathrm{AgCl}_{(\mathrm{s})}+\mathrm{NaNO}_{3(\mathrm{aq})}

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(

2

)

\mathrm{H}_{2} \mathrm{CO}_{3(\mathrm{aq})} \rightarrow \mathrm{H}_{2} \mathrm{O}_{(\ell)}+\mathrm{CO}_{2(\mathrm{~g})}

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(

3

)

\mathrm{NaOH}_{(\mathrm{aq})}+\mathrm{HCl}_{(\mathrm{aq})} \rightarrow \mathrm{NaCl}_{(\mathrm{aq})}+\mathrm{H}_{2} \mathrm{O}_{(\ell)}

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(

4

)

\mathrm{Mg}_{\text {(s) }}+2 \mathrm{HCl}_{\text {(aq) }} \rightarrow \mathrm{MgCl}_{\text {(aq) }}+\mathrm{H}_{2(\mathrm{~g})}

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1

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2

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3

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4

Identify Redox Reaction: Identify the redox reaction by looking for changes in oxidation states of elements in the reactions.
Check Equation: Check equation ( $1$ ) $\text{AgNO}_3(\text{aq}) + \text{NaCl}(\text{aq}) \rightarrow \text{AgCl}(\text{s}) + \text{NaNO}_3(\text{aq})$ . $\text{Ag}$ goes from $+1$ to $0$ , and $\text{Cl}$ goes from $-1$ to $0$ . This is a redox reaction.
Final Confirmation: No need to check further, as we found a redox reaction in step $2$ .