The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
Alzheimer's disease is an irreversible, progressive brain disease that slowly destroys memory and disorders cognitive function( remember, problem-solve, and pay attention etc).
Alzheimer's disease is mostly associated with symptoms of dementia because Alzheimer's disease is caused due to the destruction of a vast number of neurons in the hippocampus part of the brain.
So, the correct option is 'Both Assertion and Reason are correct and Reason is the correct explanation for Assertion'.