What is the conduction of an action potential at the Nodes of Ranvier called?

Regarding the $Na^+ - K^+$ pump:
$(A)$ It transports $3\, Na^+$ ions inside and $2\, K^+$ ions outside.
$(B)$ It maintains the ionic gradient through active transport.
$(C)$ It works against the concentration gradient.
Which of the above statements are incorrect?

Conduction of an impulse along the axon is associated with the

What happens during depolarization of the nerve membrane?

Which has the highest speed of nerve impulse?

Propagation of action potential is very fast in nerve fibres which have