Which of the following method is used to produce Oxygen gas in laboratory?

Question

Accepted Answer

The correct answer is: **4. (1) and (3) both**

### Explanation:

1. **Heating of KClO3 with MnO2**: 
   - When potassium chlorate (KClO3) is heated in the presence of manganese dioxide (MnO2), it decomposes to produce potassium chloride (KCl) and oxygen gas (O2). The reaction can be represented as:
     $$
     2 \, KClO_3 \, (s) \xrightarrow{heat} 2 \, KCl \, (s) + 3 \, O_2 \, (g)
     $$
   - This method is a common laboratory procedure to generate oxygen gas.

2. **Electrolysis of H2O**: 
   - Electrolysis involves passing an electric current through water (H2O) to break it down into hydrogen gas (H2) and oxygen gas (O2). The reaction can be represented as:
     $$
     2 \, H_2O \, (l) \xrightarrow{electricity} 2 \, H_2 \, (g) + O_2 \, (g)
     $$
   - This is another widely used method in laboratories to produce oxygen gas.

3. **Photosynthesis**: 
   - Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, using carbon dioxide (CO2) and water (H2O) to produce glucose and oxygen. The general equation for photosynthesis is:
     $$
     6 \, CO_2 \, (g) + 6 \, H_2O \, (l) \xrightarrow{light} C_6H_{12}O_6 \, (s) + 6 \, O_2 \, (g)
     $$
   - While this process does produce oxygen, it occurs in living organisms and is not a laboratory method per se.

4. **(1) and (3) both**: 
   - Since both the heating of KClO3 with MnO2 and the electrolysis of water are laboratory methods to produce oxygen gas, and photosynthesis is a natural process that also produces oxygen, the correct answer is that both methods (1) and (3) can be considered for producing oxygen gas in a broader sense.

### Conclusion:
Thus, the correct answer is option 4, as it includes both the laboratory methods (1 and 2) that produce oxygen gas.