Which of the following is true for marginal revenue and total revenue?

The marginal revenue curve is upward sloping while the total revenue curve is a straight line.
The total revenue curve is the inverse of marginal revenue curve.
Total revenue is at its maximum when marginal revenue is zero.Correct
Marginal revenue is equal to total revenue divided by the total number of units produced.

Explanation
Maximum revenue occurs where marginal revenue equals zero. This is because a marginal revenue of 0 lies between positive and negative marginal revenue.