Which of the following gas is released at anode in chlor-alkali process?

Chlorine

The correct answer is option 2. Chlorine.

In the chloralkali process, which is an industrial electrolysis process, aqueous sodium chloride (brine) is electrolyzed to produce chlorine gas ($\text{Cl}_2$), hydrogen gas ($\text{H}_2$), and sodium hydroxide ($\text{NaOH}$). The process takes place in an electrolytic cell equipped with a cathode and an anode.

At the anode:
- Chloride ions ($\text{Cl}^-$) are oxidized (lose electrons) to form chlorine gas ($\text{Cl}_2$).
- The half-reaction occurring at the anode is: $2\text{Cl}^- \rightarrow \text{Cl}_2(g) + 2\text{e}^-$

At the cathode:
- Water molecules ($\text{H}_2\text{O}$) are reduced (gain electrons) to form hydrogen gas ($\text{H}_2$) and hydroxide ions ($\text{OH}^-$).
- The half-reaction occurring at the cathode is: $2\text{H}_2\text{O}(l) + 2\text{e}^- \rightarrow \text{H}_2(g) + 2\text{OH}^-$

Overall reaction:
$2\text{NaCl(aq)} + 2\text{H}_2\text{O}(l) \rightarrow \text{Cl}_2(g) + \text{H}_2(g) + 2\text{NaOH(aq)}$

Chlorine gas is collected at the anode compartment, while hydrogen gas is collected at the cathode compartment. Sodium hydroxide, a valuable industrial chemical, is formed in the electrolyte (brine) solution.

Therefore, in the chlor-alkali process, chlorine gas is released at the anode.