Option 1 states that when marginal revenue is positive, total revenue increases with an increase in output. This statement is correct because marginal revenue measures the additional revenue generated from selling one more unit of output. When marginal revenue is positive, it means that the revenue from selling an additional unit is greater than the cost of producing that unit, resulting in an increase in total revenue.

Option 2 states that when marginal revenue is zero, total revenue is maximum. This statement is incorrect. When marginal revenue is zero, it means that the revenue from selling an additional unit is equal to the cost of producing that unit. At this point, total revenue is not maximum but at its peak. Total revenue could continue to increase as long as marginal revenue is positive, even if it is decreasing.

Option 3 states that when marginal revenue becomes negative, total revenue falls with an increase in output. This statement is correct. When marginal revenue becomes negative, it means that the revenue from selling an additional unit is less than the cost of producing that unit. This leads to a decrease in total revenue since the cost of production outweighs the revenue generated.

In conclusion, options 1, 2, and 3 are correct, so the correct answer is option 4.