What is the speed of nerve impulse conduction in mammalian nerve fibers?

$A$: In the nervous system,the generation of an action potential depends upon the influx of sodium ions into the axoplasm.
$R$: The influx of sodium ions during nerve impulse generation is due to the efflux of potassium ions.

What is action potential?

During resting potential,the axonal membrane is polarised. Indicate the movement of $+ve$ and $-ve$ ions leading to polarisation diagrammatically.

Select the correct sequence of statements regarding the conduction of a nerve impulse and select the correct option given below.
$i.$ Rapid influx of $Na^{+}$ inside the axon.
$ii.$ $Na^{+}$ gates are closed and $K^{+}$ gates open after the refractory period.
$iii.$ Intracellular fluid is electronegative and the potential difference is $-70 \ mV$.
$iv.$ Extracellular fluid becomes electronegative.
$v.$ Disturbance to the resting potential.

What is the nature of the reversal potential in a neuron?