आयातित वस्तु की प्रति भौतिक इकाई पर लगाया गया एक निश्चित शुल्क क्या कहलाता है?

Under the large country assumption, when a nation imposes an optimal tariff, what is the net marginal welfare effect at the optimal tariff level on the importing country?

Which of the following statements regarding tariffs are correct? 1. The level of tariff at which the welfare of the importing country reaches maximum is known as 'prohibitive tariff'. 2. The level of tariff at which the welfare of the importing country reaches maximum is known as 'optimum tariff'. 3. Prohibitive tariff produces autarky level of welfare. 4. The 'optimum tariff' is the level of tariff that minimizes deadweight loss without any terms-of-trade gain.