Is there any relationship between marginal revenue curve and demand curve?

Yes, there is a relationship between the marginal revenue curve and the demand curve. For a monopolistic firm, the marginal revenue curve lies below the demand curve because the firm must lower the price on all units sold to sell additional units, resulting in diminishing marginal revenue. In contrast, for a perfectly competitive firm, the marginal revenue curve is horizontal and coincides with the demand curve, as the firm can sell any quantity at the market price without affecting it. Thus, while the two curves are related, their positions and shapes differ based on the market structure.