Final answer:
Alzheimer's disease is the most common cause of neurocognitive disorder.
Step-by-step explanation:
The most common cause of neurocognitive disorder among the given options is Alzheimer's disease. Alzheimer's disease is a neurodegenerative disease that is characterized by the accumulation of beta-amyloid plaques, which are dense conglomerations of a protein that is not functioning correctly. This accumulation leads to neurodegeneration, particularly within the ventricles and hippocampus of the brain.