The correct answer is (c).
A Tobin tax is a tax levied on all foreign exchange transactions. It is named after James Tobin, an American economist who proposed it in 1972. The tax is intended to reduce short-term speculative trading and to stabilize exchange rates.
Option (a) is incorrect because a Tobin tax is not levied on bodies creating externalities. An externality is a cost or benefit that is not paid for by the person who causes it. For example, if a factory pollutes the air, the people who live near the factory may suffer from health problems. The factory does not pay for these health problems, so they are an externality.
Option (b) is incorrect because a Tobin tax is not levied on the basis of weight. A tax levied on the basis of weight is called a weight tax. Weight taxes are often used to discourage the use of certain products, such as gasoline.
Option (d) is incorrect because a Tobin tax is not levied on the basis of value. A tax levied on the basis of value is called a value-added tax. Value-added taxes are often used to raise revenue for governments.