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

The mineral necessary for nervous conduction is

An action potential in a nerve fiber is generated when the $+ve$ and $-ve$ charges on the outside and inside of the axon membrane are reversed because ...........

Chronaxie is defined as:

An action potential in a nerve fiber is generated when the outer surface is positive and the inner surface is negative,and the membrane potential is reversed because...

Assertion: The imbalance in concentration of $Na^+$,$K^+$ and proteins generates resting potential.
Reason: To maintain the unequal distribution of $Na^+$ and $K^+$,the neurons use electrical energy.