Choose the incorrect statement.

Options

A. We are encouraged to plant more trees so as to ensure clean environment and also provide biomass fuel
B. Gobar-gas is produced when crops, vegetable wastes etc., decompose in the absence of oxygen
C. The main ingredient of biogas is ethane and it gives a lot of smoke and also produces a lot of residual ash
D. Bio-mass is a renewable source of energy

Explanation

To solve the question "Choose the incorrect statement," we will analyze each option provided in the video transcript step by step.

### Step-by-Step Solution:

1. **Analyze Option A**:
- The statement is: "We are encouraged to plant more trees so as to ensure a clean environment and to also provide biomass fuel."
- This statement is correct because planting trees contributes to a clean environment and trees can be used as a source of biomass fuel.

2. **Analyze Option B**:
- The statement is: "Biogas is produced when crops, vegetable waste, etc., decompose in the absence of oxygen."
- This statement is also correct. Biogas is indeed produced through anaerobic decomposition, which occurs in the absence of oxygen.

3. **Analyze Option C**:
- The statement is: "The main ingredient of biogas is ethane, and it gives a lot of smoke and also produces a lot of residual ash."
- This statement is incorrect. The main ingredient of biogas is methane, not ethane. Methane is a cleaner fuel that produces less smoke and minimal residual ash compared to ethane.

4. **Analyze Option D**:
- The statement is: "Biomass is a renewable source of energy."
- This statement is correct. Biomass is considered a renewable source of energy because it can be replenished over time through natural processes.

### Conclusion:
- The incorrect statement is **Option C**: "The main ingredient of biogas is ethane, and it gives a lot of smoke and also produces a lot of residual ash."