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

Assertion (A): The neurons of neural system are excitable cells.

Reason (R): Differential concentration gradient of ions is present across membranes. 

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

Assertion (A) is true. The neurons of neural system are excitable cells. They can generate and transmit electrical signals in response to various stimuli, such as changes in ion concentrations or the binding of neurotransmitters.

Reason (R) is true. Differential concentration gradient of ions is present across membranes. Neurons maintain differential concentration gradients of ions, particularly sodium (Na⁺), potassium (K⁺), and chloride (Cl^-), across their cell membranes. This is essential for the generation and propagation of electrical signals, as it allows for changes in membrane potential and the transmission of signals through the nervous system.