Step 1: Understanding the question.
According to Indian planning standards, a medical college should be established in areas with a significant population to ensure its viability and serviceability. The planning standards set the threshold population for such institutions.
Step 2: Analyzing the options.
(A) 500000: This population threshold is not sufficient for planning a medical college according to Indian standards.
(B) 1000000: Correct — A medical college is to be provided for planning units with a minimum population of 1 million, as per Indian planning standards.
(C) 10000000: This is too large, as the threshold is set at 1 million, not 10 million.
(D) 2500000: This is incorrect, as the population requirement is lower than 2.5 million.
Step 3: Conclusion.
The correct answer is (B) 1000000, as per Indian planning standards for the establishment of medical colleges.