A notable change in Nagaland’s population since the 1951 Census is:

The correct answer is: d) A large increase in the female population.

Nagaland’s population has increased significantly since the 1951 Census. The sex ratio has also changed, with the number of females per 1000 males increasing from 935 in 1951 to 975 in 2011. This increase is due to a number of factors, including improved healthcare and education, as well as a decline in the practice of female infanticide.

The other options are incorrect. Option a) is incorrect because the population density of Nagaland has increased since the 1951 Census. Option b) is incorrect because the sex ratio of Nagaland has improved since the 1951 Census. Option c) is incorrect because the rate of urbanization in Nagaland has been relatively slow.

Here is a brief explanation of each option:

• A decrease in population density. The population density of Nagaland is the number of people living in a given area. It is calculated by dividing the total population by the total area of the state. The population density of Nagaland has increased since the 1951 Census. In 1951, the population density of Nagaland was 12 people per square kilometer. In 2011, the population density of Nagaland was 17 people per square kilometer. This increase is due to a number of factors, including natural population growth and immigration.
• A decline in the sex ratio. The sex ratio is the number of females per 1000 males. The sex ratio of Nagaland has improved since the 1951 Census. In 1951, the sex ratio of Nagaland was 935 females per 1000 males. In 2011, the sex ratio of Nagaland was 975 females per 1000 males. This improvement is due to a number of factors, including improved healthcare and education, as well as a decline in the practice of female infanticide.
• Rapid urbanization. Urbanization is the process of people moving from rural areas to urban areas. The rate of urbanization in Nagaland has been relatively slow. In 1951, the urban population of Nagaland was 10% of the total population. In 2011, the urban population of Nagaland was 20% of the total population. This slow rate of urbanization is due to a number of factors, including the state’s mountainous terrain and its relatively small population.