This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Errors and P-Value, Subject name: Social & Preventive Medicine
In a population of 100000, hemoglobin of 100 women is estimated with standard deviation of 2gm%. What is the standard error - 
Select and explain. 
A. 1, B. 0.1, C. 2, D. 0.2
D: 0.2
Answer: D: 0.2 
Explanation: Ans. is 'd' i.e., 0.2