Explanation:

- If a firm increases its output from Q2 to Q1:

- Option 1: Reduce its marginal revenue

- This could occur if the demand curve is downward sloping, making each additional unit bring in less revenue than the previous one.

- Option 2: Increase its profit

- Increased output can lead to higher total revenue, but might also increase costs, so profit could rise or fall, depending on these factors.

- Option 3: Increase its marginal revenue

- Unlikely if the demand is inelastic as increasing quantity would generally lower marginal revenue.

- Option 4: Decrease its profit

- This could happen if the marginal cost of producing additional units is higher than the marginal revenue received.

Option 4: Decrease its profit