1.Morbidity is a term used to describe the state of being unhealthy or diseased, and it specifically refers to the incidence or prevalence of illnesses or diseases within a population. Morbidity measures the extent to which people in a particular area or population are prone to falling ill or experiencing health issues. It is a crucial indicator of the health status of a community or society.

2.Sanitation, on the other hand, primarily relates to the provision of clean and hygienic conditions, such as proper waste disposal, clean water supply, and sanitary facilities, to prevent the spread of diseases and maintain public health. While sanitation is important for preventing morbidity, it is not the same as morbidity. Sanitation focuses on creating conditions that reduce the risk of illness, while morbidity refers to the actual occurrence or prevalence of illness.

3.The "Global Burden of Disease" is a comprehensive study that assesses the impact of diseases and injuries on a global scale, measuring both morbidity and mortality (deaths). So, while it is related to morbidity, it encompasses a broader perspective, including the overall health impact of diseases and injuries.

In the context of the question, "proneness to fall ill" directly relates to morbidity, which is why option (3) "Morbidity" is the correct answer.