The correct answer is: a) Overgrazing.
Overgrazing is the removal of too much vegetation by grazing animals. This can lead to a number of problems, including soil erosion, loss of biodiversity, and changes in water quality. Overgrazing is a major challenge to soil health in Nagaland, as it can lead to the degradation of the soil and the loss of its ability to support plant life.
Deforestation is the clearing of forests for other uses, such as agriculture, development, or logging. This can also lead to soil erosion and loss of biodiversity. However, deforestation is not as significant a challenge to soil health in Nagaland as overgrazing.
Excessive irrigation can also lead to soil erosion and loss of nutrients. However, this is not as common a problem in Nagaland as overgrazing or deforestation.
Industrial pollution can also damage soil health. However, this is not as significant a problem in Nagaland as overgrazing, deforestation, or excessive irrigation.
In conclusion, overgrazing is the major challenge to soil health in Nagaland. This is because it can lead to a number of problems, including soil erosion, loss of biodiversity, and changes in water quality.