Assertion : When a neuron is not conducting any impulse, i.e. resting, the axoplasm inside the axon contains high concentration of `K^(+)` and negatively charged proteins and low concentration of `Na^(+)`.
Reason : In resting, the axonal membrane is comparatively more permeable to `K^(+)` ions and nearly impermeable to `Na^(+)` ions. Similarly, the membrane is impermeable to negatively charged proteins present in axoplasm

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 the Assertion**: The assertion states that when a neuron is at rest (not conducting any impulse), the axoplasm (the cytoplasm within the axon) has a high concentration of potassium ions (K⁺) and negatively charged proteins, while having a low concentration of sodium ions (Na⁺).

2. **Analyzing the Reason**: The reason provided explains that during the resting state, the axonal membrane is more permeable to potassium ions and nearly impermeable to sodium ions. It also mentions that the membrane is impermeable to negatively charged proteins present in the axoplasm.

3. **Resting Membrane Potential**: In a resting neuron, the membrane potential is polarized. This polarization occurs because of the distribution of ions across the membrane. The high concentration of K⁺ inside and Na⁺ outside the neuron contributes to this polarization.

4. **Ion Permeability**: The resting membrane is primarily permeable to K⁺ ions due to the presence of potassium channels that allow K⁺ to flow out of the neuron. In contrast, sodium channels are mostly closed, preventing Na⁺ from entering the neuron. This differential permeability is crucial for maintaining the resting membrane potential.

5. **Negatively Charged Proteins**: The negatively charged proteins inside the axoplasm cannot cross the membrane, contributing to the overall negative charge inside the neuron compared to the outside.

6. **Conclusion**: Both the assertion and the reason are true. The assertion correctly describes the ionic concentrations in the resting state of a neuron, and the reason accurately explains why these concentrations exist due to the permeability characteristics of the axonal membrane.

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

---