Explanation:

- The Planning Commission in India has used calorie intake as one of the criteria to define the poverty line.

- For urban areas, the recommended nutritional necessity is 2,100 calories per person per day.

- This measure helps to assess the minimum consumption required to maintain health.

- Option 1: 3,000 calories – This is higher than the average recommendation for urban areas.

- Option 2: 2,500 calories – This is a more typical recommendation for some rural areas, not urban.

- Option 3: 3,100 calories – This is not used as a standard for urban poverty lines.

- Option 4: 2,100 calories – Correct and commonly used by the Planning Commission for urban poverty assessment.