The marginal revenue curve for a monopoly firm is downward sloping from left to right. This shows that when more commodities are brought in the market, the price falls and therefore the additional revenue (MR) reduces as more output is sold.

It is also observed from the above that the marginal revenue curve lies below the demand curve. This follows from the rule that when the average  (AR) is falling, the margin (MR) is below the average.