Concept:A free trade area is the form of economic integration in which member nations remove tariffs on trade among themselves but remain free to set their own tariffs against non-member countries.
Explanation:In a free trade area, member countries trade with one another without customs duties.
Each member nation is therefore free to impose its own duty on goods coming from non-members.
A customs union is incorrect because its members must apply one common external tariff.
A common market is incorrect because it also uses a common external tariff and allows free movement of labour and capital.
An economic community is incorrect because it involves deeper harmonisation of economic policies among members.
So the integration type that leaves every member nation free to fix its own duties against non-members is the free trade area.
Answer:B. Free trade area