Assertion : Neurons are excitable cells.
Reason : The membrane of the neurons are in a polarised state.

Options

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Explanation

### Step-by-Step Solution:

1. **Understanding Neurons**: Neurons are specialized cells that make up the nervous system. They are responsible for transmitting signals throughout the body.

2. **Definition of Excitable Cells**: Excitable cells are those that can generate and propagate electrical signals. Neurons fall into this category because they can respond to stimuli and transmit impulses.

3. **Polarized State of Neuronal Membranes**: The membrane of a neuron is said to be in a polarized state when there is a difference in charge across the membrane. In a resting neuron, the inside of the cell is negatively charged relative to the outside, which is positively charged.

4. **Mechanism of Polarization**: This polarization is maintained by the distribution of ions, primarily sodium (Na+) and potassium (K+), across the neuronal membrane. The presence of ion channels allows for the movement of these ions, contributing to the excitability of the neuron.

5. **Linking Assertion and Reason**: The assertion states that "Neurons are excitable cells," and the reason given is "The membrane of the neurons are in a polarized state." Since the polarized state of the membrane is what allows neurons to be excitable, the reason supports the assertion.

6. **Conclusion**: Both the assertion and the reason are correct, and the reason provided is a valid explanation for why neurons are considered excitable cells.

### Final Answer:
Both the assertion and the reason are true, and the reason is the correct explanation for the assertion.