Questions: All of the following describe perfectly competitive firms, except each produces a negligible share of industry output they produced standardized products they make no attempt to differentiate their products they face large barriers to entry

The answer is the last one: they face large barriers to entry.

Explanation for each option:

1. Each produces a negligible share of industry output: This is correct for perfectly competitive firms. In a perfectly competitive market, there are many small firms, each producing a small fraction of the total market output, so no single firm can influence the market price.

2. They produce standardized products: This is also correct. Perfectly competitive firms produce homogeneous or standardized products, meaning that the products are identical and interchangeable with those of other firms in the market.

3. They make no attempt to differentiate their products: This is correct as well. In perfect competition, firms do not differentiate their products because the products are standardized, and consumers perceive them as identical.

4. They face large barriers to entry: This is incorrect for perfectly competitive firms. In a perfectly competitive market, there are no significant barriers to entry or exit. Firms can freely enter or leave the market based on their economic interests.

In summary, the characteristic that does not describe perfectly competitive firms is that they face large barriers to entry.