Assertion: Xerarch succession ultimately leads to mesic conditions.
Reason: Xerarch succession begins on rocks.

The correct option is B Both the assertion and reason are true but the reason is not the correct explanation for the assertion
Ecological succession is a steady, gradual change in the composition and structure of communities of an area with the changing environment. It is predictable, sequential and occurs in accordance with the changing physical environment.
Xerarch succession is a type of ecological succession which progresses from xeric (very dry) conditions such as rocks, deserts, etc., to mesic (medium water) conditions.