Explanation:

- Initial Revenue Calculation: Revenue is the product of tax and consumption. Represent this as \( R = T \times C \), where \( T \) is the tax per unit and \( C \) is the consumption.

- Reduction in Tax: If the tax on the commodity is reduced by 20%, the new tax rate is \( 0.8T \).

- Increase in Consumption: Consumption increases by 15%, making the new consumption \( 1.15C \).

- Effect on Revenue: The new revenue becomes:

\((0.8T) \times (1.15C) = 0.92 \times (T \times C)\).

- Revenue Change: This indicates a fall in revenue by 8% (from 1 to 0.92).

- Correct Answer: Therefore, the revenue decreases by 8%.

- ?? Option 1: 8% is correct.