The real cost of a commodity is:

Explanation

The question is asking about the definition of the real cost of a commodity. The real cost refers to the actual cost of a commodity, which is not just the market price. Option A states that the real cost is the cost of the alternative that has to be sacrificed for it. This means that if you choose to buy one thing, you have to give up the opportunity to buy another thing. Option B is the correct answer, which states that the real cost is the alternative cost involved when the opportunity of buying the commodity is mixed. This means that the real cost is the cost of the next best alternative that you have to give up in order to buy the commodity.

Option C states that the real cost is its market price. This is not entirely correct because the market price is just one aspect of the real cost. Option D states that the real cost is the alternative that has to be forgone in order to purchase it. This is similar to Option A, but it is not specific enough because it does not mention the opportunity cost.

Understanding the concept of opportunity cost is essential in economics. Opportunity cost refers to the value of the next best alternative that must be given up in order to engage in an activity. For example, if you choose to attend a football game, the opportunity cost is the value of the next best alternative use of your time, such as studying or working.

In summary, the real cost of a commodity is the alternative cost involved when the opportunity of buying the commodity is mixed. This means that the real cost is the cost of the next best alternative that you have to give up in order to buy the commodity.