Step 1: Understanding the Concept.
India's poverty line was first drawn using a minimum calorie intake a person needs each day, and this minimum was set separately for villages and cities.
Step 2: Key Formula or Approach.
Recall the two benchmark numbers used by the Planning Commission: rural areas use 2400 kcal per person per day, and urban areas use a lower figure because city work is assumed to need less physical energy.
Step 3: Detailed Explanation.
The question already states the rural figure as 2400 kcal. The matching urban figure fixed by the same calculation is 2100 kcal per person per day. The options 1900 and 2800 do not correspond to any official calorie line, and 2400 is simply the rural value repeated, not the urban one.
Step 4: Final Answer.
The urban poverty line calorie limit is 2100 kcal per day.
\[ \boxed{2100} \]