Explanation:

- The Census of India is conducted every ten years.

- The first complete census took place in 1881, making it a longstanding practice to gather comprehensive population data.

- Option 1: 11th - This suggests a much earlier count, which would have been around the mid-20th century.

- Option 2: 20th - This would be too advanced for the 2011 census as it occurs every decade.

- Option 3: 17th - This falls between the two extremes but doesn't align with the sequential order.

- Option 4: 15th - The 2011 Census was indeed the 15th National Census of India.