Both $A$ and $R$ true and $R$ is the correct explanation of $A .$
When a neuron is not conducting any impulse, i.e., resting, the axonal membrane is comparatively more permeable to potassium ions $\left(K^{+i i}\right)$ and nearly impermeable to sodium ions $\left(N a^{+i i}\right) .$ Similarly, the membrane is impermeable to negatively charged proteins present in the axoplasm. Consequently, the axoplasm inside the axon contains high concentration of $K^{+i i}$ and negatively charged proteins and low concentration of $N a^{+i i} .$ In contrast, the fluid outside the axon contains a low concentration of $K^{+i i}$, a high concentration of $N a^{+i i}$ and thus form a concentration gradient
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$\begin{array}{|l|l|} \hline Column\,\,-I & Column\,\,-II \\ \hline (a)\,\,Hinge\,\,joint & (1)\,\,Between\,\,atlas\,\,and\,\,axis \\ \hline (b)\,\,Pivot\,\,joints & (2)\,\,Humerus\,\,and\,\,wrist \\ \hline (c)\,\,Ball\,\,and\,\,rocket\,\,joint & (3)\,\,Knee\,\,joint \\ \hline (d)\,\,Gliding\,\,joint & (4)\,\,Shoulder \\ \hline \end{array}$
$\begin{array}{|l|l|} \hline Column\;-\;I & Column\;-\;II \\ \hline A.\;Caecum\;in\;earthworm & 1.\;Tubular \\ \hline B.\;Caecum\;in\;cockroach & 2.\;Forgut \\ \hline C.\;Gizzard\;in\;earthworm & 3.\;26^{th}\;segment \\ \hline D.\;Gizzard\;in\;cockroach & 4.\;8-9\;segment \\ \hline \end{array}$