Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R).

Assertion (A) : Nodes of Ranvier are not observed in the axons of unmyelinated nerve fibres.

Reason    (R)  : Axons of nerve fibers lack Nissl's granules.

In light of the above statements, choose the correct answer from the options given below.

Both (A) and (R) are true but (R) is not the correct explanation of (A).

Nodes of Ranvier are not observed in the axons of unmyelinated nerve fibers. Nodes of Ranvier are the gaps between myelin sheaths in myelinated nerve fibers, and since unmyelinated fibers lack myelin sheaths, they also lack Nodes of Ranvier.
Axons of nerve fibers lack Nissl's granules. Nissl's granules are found in the cell bodies of neurons, not in their axons. This is true for both myelinated and unlyelinated nerve fibres. However, the absence of Nissl's granules in the axons is not directly related to the presence or absence of Nodes of Ranvier.