Concept:A customs union removes internal trade barriers and applies a common external tariff to non-members.Explanation:The key feature described is the removal of all trade barriers between member countries.At the same time, members adopt a unified external tariff against non-member nations.A free trade area removes internal barriers but each member keeps its own external tariffs.A common market adds free movement of labour and capital, and an economic union adds policy coordination.Since the statement focuses only on internal free trade plus a common external tariff, it matches a customs union.Answer:Custom union (Option B).