Let's analyze the given chemical reaction and the associated half-reactions to determine which one correctly represents the reduction process.
The full reaction is:
[tex]\[ Zn (s) + 2 H^+ (aq) \longrightarrow Zn^{2+} (aq) + H_2 (g) \][/tex]
In any redox reaction, there are two processes occurring: oxidation and reduction.
Oxidation involves the loss of electrons:
[tex]\[ \text{Zn (s)} \rightarrow \text{Zn}^{2+} \text{(aq)} + 2 e^- \][/tex]
Reduction involves the gain of electrons. Here, we need to determine which species gains electrons. The evolution of hydrogen gas (\( H_2 \)) suggests that \( H^+ \) ions gain electrons to form \( H_2 \) gas.
So we look for the half-reaction where \( H^+ \) gains electrons. The options provided are:
1. \( Zn (s) \longrightarrow Zn^{2+} (aq) + 2 e^- \)
2. \( 2 H^+ (aq) + 2 e^- \longrightarrow H_2 (g) \)
3. \( Zn (s) \longrightarrow Zn^{2+} (aq) + e^- \)
4. \( 2 H^+ (aq) + e^- \longrightarrow H_2 (g) \)
Among these, option 2 correctly represents the reduction half-reaction:
[tex]\[ 2 H^+ (aq) + 2 e^- \longrightarrow H_2 (g) \][/tex]
This half-reaction shows that hydrogen ions (\( H^+ \)) gain electrons to form hydrogen gas (\( H_2 \)).
Thus, the correct half-reaction representing reduction in the given chemical equation is:
[tex]\[ 2 H^+ (aq) + 2 e^- \longrightarrow H_2 (g) \][/tex]
And correspondingly, the correct option is:
[tex]\[ 2 \][/tex]
