In which state is a polarized nerve fiber found?

Which of the following processes are responsible for the transport of $Na^+$ from outside to the inner side of the axon membrane during the generation of a nerve impulse?

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 ...........

The potential difference in the membrane,which is responsible for the conduction of an impulse,is brought about by a change in the membrane:

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

If the inside of the membrane becomes more negative,it leads to: