If a firm finds it most profitable to adopt the same strategy regardless what its rival chooses to do, then that firm has a dominant strategy

Step 1: Read the question carefully and understand what is being asked.

Step 2: Identify the key terms in the question, such as "profitable," "strategy," and "dominant strategy."

Step 3: Read each answer option and determine if it accurately describes a dominant strategy.

• "If a firm finds it most profitable to adopt the same strategy regardless of what its rival chooses to do, then that firm has a dominant strategy" is a correct definition of a dominant strategy. It means that the firm has a strategy that is always the best choice, regardless of what its rival does.
• "All firms in a market have a dominant strategy" is not necessarily true. It is possible that no firm has a dominant strategy, or that only one firm has a dominant strategy.
• "A dominant strategy is only possible in a perfectly competitive market" is not true. Dominant strategies can exist in any type of market.
• "A dominant strategy is the same as a Nash equilibrium" is not true. A Nash equilibrium is a situation where no player can improve their payoff by changing their strategy, but it does not necessarily mean that there is a dominant strategy.

Step 4: Based on the above analysis, the correct answer is "If a firm finds it most profitable to adopt the same strategy regardless of what its rival chooses to do, then that firm has a dominant strategy."