I'd like you to explain about these questions from Microeconomics perspective for my study.

1.Since a perfectly competitive firm can sell as much as it wishes at the market price, why can the firm not simply increase its profits by selling an extremely high quantity?

2.Assuming that the market for cigarettes is in perfect competition, what does allocative and productive efficiency imply in this case? What does it not imply?

3.Why will profits for firms in a perfectly competitive industry tend to vanish in the long run?