The correct answer is option 1: 1911-21. This means that between the years 1911 and 1921, India experienced a negative growth rate of population.

A negative growth rate of population refers to a decrease in the population over a specific time period. It indicates that the number of deaths and outmigration from a region exceeded the number of births and immigration into the region.

Option 2: 1921-31 refers to the following decade, and it is not the correct answer provided in the question.

Option 3: 1931-41 refers to yet another decade, and it is also not the correct answer provided in the question.

Option 4: 1941-51 refers to another decade after the correct answer period and is not the correct answer either.

It is important to note that a negative growth rate of population is relatively uncommon and indicates a decline in population. These periods are significant for studying demographic changes, as they reflect specific socioeconomic and environmental factors that influenced population dynamics in India.