It's an external cost.

It's an external benefit

It can be both an external cost and an external benefit.

A subsidy to a merit good will reduce its price and increase consumption and this will be beneficial to the individual and society; while an indirect tax on a demerit good will raise the price, reduce consumption and limit the potential damage to the individual and society.

A subsidy to a merit good will increase its price and reduce consumption and this will be beneficial to the individual and society; while an indirect tax on a demerit good will reduce the price, raise consumption and limit the potential damage to the individual and society.

Direct taxation is a payment made out of the income and/or wealth of individuals or the income (profits) of a firm. Indirect taxation is usually referred to as expenditure taxation as it is paid on the purchase of specified products and is therefore made only at the point of consumption.

Direct taxation is usually referred to as expenditure taxation as it is paid on the purchase of specified products and is therefore made only at the point of consumption. Indirect taxation is a payment made out of the income and/or wealth of individuals or the income (profits) of a firm.

The optimal output for society will be more than the actual output.

the optimal output for society will be less than the actual output.

The optimal output for society cannot be known without more precise information.

Drugs given under prescription are not a demerit good.

Drugs gained otherwise than prescription are not a demerit good.