Final answer:
In competitive markets, firms are less likely to invest in advertising due to the homogeneity of products, but they may still do so in monopolistic competition to differentiate their offerings. Successful advertising can make the perceived demand curve for a firm's product more inelastic or shift it to the right.
Step-by-step explanation:
It is less common for individual firms in competitive markets to invest in advertising because they sell homogeneous products. Advertising in this market increases market awareness without directly influencing sales. However, firms will still advertise to increase demand for the common product.
Advertising in competitive markets is a way for firms to differentiate themselves from their competitors. In a monopolistic competition, advertising can make a firm's perceived demand curve become more inelastic (steeper) or increase overall demand for the firm's product (shifting the demand curve to the right). A successful advertising strategy may lead to increased profits by allowing the firm to charge higher prices or sell larger quantities.