Long-run in economic mean a period of time in which

Step 1: Analyze the question The question asks for the definition of the "long run" in economics, a basic concept from the theory of production and cost.

Step 2: Explain the concept In economics, time periods are classified by whether firms can change their inputs:

• Short run: a period in which at least one factor of production is fixed (for example, land, factory size or heavy machinery), while others such as labour and raw materials can be changed.
• Long run: a period long enough for a firm to change all its factor inputs. Nothing is fixed. The firm can build a bigger factory, buy new machines, or leave the industry altogether.

The length of the long run differs between industries. A roadside tailor can expand in weeks, while an oil refinery may need years.

Step 3: Test each option

• A. All factor inputs are not being used: This has nothing to do with time. It describes idle resources or underutilisation. ❌
• B. All factor inputs are variable: This matches the definition of the long run exactly. ✅
• C. All factor inputs are fixed: This describes the very short run or market period, where supply cannot be changed. ❌
• D. Only few factor inputs are variable: This describes the short run, where some inputs are fixed and some are variable. ❌
• E. Firms are not producing at all: Production continues in both the short and long run. ❌

Step 4: Answer

Step 5: Exam tip Remember it this way: "Long run = Lots of change." In the long run, everything is variable. In the short run, something is stuck (fixed). If an option says "all factors are variable," it is almost always the long-run definition.