Assertion (A): In our actions of writing or talking, our nervous system communicates with the muscles.

Reason (R): Cranial nerves and spinal nerves form the peripheral nervous system.

The chapter states: "We also think about our actions. Writing, talking, moving a chair, clapping at the end of a programme are examples of voluntary actions which are based on deciding what to do next. So, the brain also has to send messages to muscles. This is the second way in which the nervous system communicates with the muscles. The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system consisting of cranial nerves arising from the brain and spinal nerves arising from the spinal cord."

Assertion (A) is TRUE: writing and talking are voluntary actions in which the nervous system (brain) communicates decisions to the muscles that carry them out.

Reason (R) is TRUE: the peripheral nervous system, made of cranial nerves (from the brain) and spinal nerves (from the spinal cord), is exactly the pathway that carries these instructions from the central nervous system (brain and spinal cord) to the muscles and back.

Since it is the cranial and spinal nerves of the peripheral nervous system that physically carry the messages from the brain to the muscles during actions like writing or talking, R correctly explains why A is true. Hence option (A) is correct.

Why the other options are wrong:

(B) is wrong because R does explain A — the peripheral nerves are precisely the communication link described in A.

(C) is wrong because Assertion (A) is true, not false — the text explicitly names writing and talking as voluntary actions where the nervous system communicates with muscles.

(D) is wrong because Reason (R) is also true, not false — cranial and spinal nerves genuinely constitute the peripheral nervous system as per the chapter.